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Will I really see photos better enough to warrant the cost?

Honestly: Probably not. Taking better photos has a lot more to do with the knowledge, experience, and creative eye of the photographer than it has to do with the minor differences between reasonably comparable lenses or camera bodies.

Unless you can articulate what it is about your two current lenses that limit your ability to create the photos you wish to create the slightly better optical quality and slightly faster maximum apertures likely won't make any real improvements in your photos. In fact, unless you are aware of the limitations and how to deal with them when using wider apertures you could actually wind up with pictures that are not even as good as you might get with your two current lenses.

The primary advantages of the three "L" lenses you are considering are in the areas of durability and resistance to adverse environmental conditions. Those attributes are critical to working pros who put their gear through the wringer every working day. Yes, they are a little better optically than your current lenses. But they are much closer to your current lenses in terms of optical performance than they are to the truly premium lenses in each category such as the EF 11-24mm f/4 L, EF 24-70mm f/2.8 L II, or the EF 70-200mm f/2.8 L IS II. Even those lenses only make a truly noticeable difference when using them at or nearly at wide open apertures. At f/5.6 or f/8 there's very little real difference.

If you really want to increase the your ability to get shots on your vacation that you can't get with your current lenses, you might consider an ultra-wide angle lens such as the EF-S 10-22mm f/3.5-4.5. But that would only be good if you are interested in capturing wider vistas than you can with your current 15-85.

There's an old saying that's been around a long time: Gear doesn't matter.
That's really only half the story.
The full truth is: Gear doesn't matter - until it does.

When the limits of your gear truly begin matter to you and where you are in your growth as a photographer you'll know it.

P.S.- The reason the 16-35mm f/4 gets better reviews is because unless you really, really, really need the f/2.8 aperture to shoot moving subjects in low light the f/4 lens is just as good or even better at all apertures above f/4. And it's cheaper to boot.