There's a more conventional answer below that was pretty much complete when I decided this needed to be said first.
Before you go running down the rabbit hole of GAS, you'll do yourself a great favor to ask yourself some hard questions.
Questions such as:
- Am I really getting the most out of what I already have? (Please read the linked answer to another question here so I'm not tempted to repeat all of it in this answer.)
- Just how much marginal improvement do I need to see in lens performance before it makes the full price of a new lens worth it to me? (Also related: Will I see enough improvement moving from EF-S to "L" lenses to warrant the cost?)
- Is my dissatisfaction with my current gear based on pixel peeping?
- Am I spending more time researching new gear I want than I am studying how past masters did what they did, much of it with less capable gear than even my entry level gear? (Seeing light, creative composition, and solid technique almost always trumps differences in gear. Photographers, not cameras, make photos.)
- Are there other photographers who get great results with the same gear I am using? (You can do a search for a specific camera or lens on Flickr that will show you images tagged with that lens. It's not perfect, but it will show you plenty of images that were taken with that lens along with some that were not.)
- Have other photographers work actually improved that noticeably when they upgraded the gear they were using?¹
All gear has limits, even the most expensive latest and greatest bodies and lenses. If you want to know what their biggest limitations are, just wait around until their replacement is announced. The manufacturer will tell you exactly how the newer model is better at x, y, and z over the previous model that sounded perfect when they introduced it a few years earlier!
Every photographer who's ever been worthy of the title "Photographer" has, at times, had feelings of 'fighting with their equipment'. That's because there's no such thing as a perfect camera, there's no such thing as a perfect lens, and there never will be! The marketing hype machines of the camera/lens makers try to make you think, "If only I had camera X and lens Y there wouldn't be any technical limitations that I would need to overcome!"
The truth is there are a lot of things many photographers would like to do that no camera/lens has the capability of doing. The thing that separates the great 'Photographers' from the complainers who always blame the limitations of their gear for their work that doesn't meet their lofty expectations based on the marketing hype of the camera makers is that the 'Photographers' learn to push the limits of the gear at their disposal while also finding ways to work just within those same limits.
The key to being an outstanding photographer is not having the best equipment in your hands. It is knowing the equipment you have well enough to know what it will and will not allow you to do and then working within those parameters to get images that the technical capabilities of the gear at your disposal will allow you to take.
¹ It will take some time, but take a look at this Flickr user's photostream. Sort by "date taken" and start at the very of the last page, where images taken with lesser gear over a decade ago were uploaded. A lot of the earliest work was done with the very limited EOS 350D - the original Digital Rebel from 2003 - and an EF-S 18-55mm lens that was nowhere near as good as the current STM version. They also used the EF-S 10-22mm that had comparable optical quality to the original 18-55mm and original EF-S 55-250mm lenses. Much of it looks like it could have been straight out of camera JPEGs. This user seems to have changed gear more often than some folks change clothes, all the way up to some very nice gear in the present. But when viewing at typical web sizes, even on my 27" desktop monitor, there's not a whole lot of noticeable difference in technical quality between the digital cameras from the 350D + 18-55mm to the R5, etc. What differences there are looks like better compositional and post-processing skills. The old film scans are an entirely different matter. Poor technique combined with slow, cheap film can be noticed almost instantly.
In addition to the linked questions and answers in the material above, here are some other existing questions and answers here at Photography SE regarding how differences in gear affect our photographic results that you might find beneficial:
Does the camera matter?
When should I upgrade my camera body? (The accepted answer equally applies to lenses, flashes, etc.)
What should I consider when shopping for a second lens (after the kit)?
P.S. I borrowed most of the second half of the above from my answer to How to know you've outgrown your equipment? You might find that question and all of its answers beneficial.
There's not much, if any difference between the optical performance of the EF 24-105mm f/4 L IS and the newer II version. When all are used on the same APS-C camera there's also not much, if any, difference between those two and the EF-S 17-55mm f/2.8 IS at focal lengths and apertures they all have in common. You can compare both an EF 24-105mm f/4 L IS and an EF-S 17-55mm f/2.8 IS used on a 7D Mark II here.
Of course the focal length range is significantly different between a 17-55mm lens and a 24-105mm lens. That basically comes down to personal preference, so only you can best answer which is better for you.
For around what you'll pay for an EF 24-70mm f/4 L, you can get a really good Tamron 24-70mm f/2.8 Di VC G2 lens. The Canon 24-70/4 is a little bit sharper and is near Macro capable at 0.70X magnification at closest focus. But the Tamron is a full stop faster and is pretty sharp too. The Tamron's minimum focus distance is nearly twice as far (381mm vs 200mm), so not so great for bugs, stamps, and coins when compared to the EF 24-70mm f/4 L IS. But as an all around general purpose zoom, I've seen some really great work done with the Tamron 24-70mm f/2.8 Di VC G2 and its immediate predecessor, the 24-70mm f/2.8 Di VC. (Full disclosure, my friend Garrick was using a Nikon version of the Tamron on his Nikon FF bodies before he went mirrorless about 4 years ago.) But then again, don't sell the kit lens too short if you're not already getting all you can out of it. Other than the first few taken with a 50mm f/1.8, this Flickr user's photos are almost all taken with an EF-S 18-55mm f/4-5.6 IS STM or the even older non-IS EF-S 18-55mm f/3.5-4.6 III.
I've used an EF 24-105mm f/4 L IS for over a decade and probably taken close to a quarter million photos with it. It's a lens that is built like a tank and will take most any punishment you can throw at it short of salt water or Burning Man (both of which will kill any camera or lens not properly protected for those environments) and just keep on working as well as it ever has.
Pretty much all of those photos, though, other than a handful of test shots to dial in AFMA in case I ever needed to use it in an emergency on one of my APS-C bodies, have been with it hanging on a FF camera. I can't imagine the same lens being near as useful to me on an APS-C body. It's simply not wide enough for me in a single lens setup, and it's no long enough to be the "long" lens in a two lens setup unless your other lens is something like a 10-22mm zoom and you never want or need to go past 105mm on APS-C (165mm FF equivalent).
(Full disclosure: since 2011 the only APS-C bodies I've used are an EOS 50D, 7D, and 7D Mark II with an EF 70-200mm f/2.8 L IS II or Sigma 120-300mm f/2.8 | S for shooting sports while using a FF camera for my "wide" body.)
When my primary cameras were APS-C bodies, my walkaround lens of choice was a Tamron 17-50mm f/2.8 Di II. I also had an EF-S 55-250mm f/4-5.6 IS II for when the 17-50mm wasn't long enough. Canon's APS-C 55-250mm lenses are optically as good as the same generation 70-300mm lenses, and MUCH better than the 75-300mm dogs or the really cheap 70-300mm lenses from Sigma and Tamron before they both upped their game beginning around 2010 or so.
An EF 24-105mm f/4 L IS (either EF version) is not going to knock your socks off with optical performance. All of my primes are sharper (EF 35mm f/2 IS, EF 50mm f/1.4, EF 85mm f/1.8, EF135mm f/2 L), but it's sharp enough for most use cases. You have to pixel peep to really see any weakness as far as acutance goes. It does have a good bit of peripheral illumination drop-off at the wider focal lengths, but then so does every other 24-70/2.8, 17-50/2.8, 17-40/4, 16-35/2.8, etc. wide angle zoom lens on the market.
Bryan Carnathan at The-Digital-Picture has a pretty in depth review of the EF-S 17-55mm f/2.8 IS, as well as just about every other Canon EOS lens released since around 2000 (and many that were released earlier but still in Canon's current catalog when he started his website).
But don't go buying such lenses just because someone else, like me, tells you to. Buy whichever one you need when you realize which one will let you do something you want to do with your camera that your current lens does not allow.
