Hmmm. I've been at this a while, and it's true that the photographer matters way more than the total camera system. However, even if one opts for a built-in lens, the complete hardware system (speed lights and tripods, etc, too) should be considered, and as a value, together.
That's not to say, there aren't some situations where it is also, the camera/system. Here's the thing though: A ridiculously high priced camera/system, is too much! Now, I know, a bigger sensor usually, has better DR, tonal gradations, color sensitivity (leading to a more pleasing pallet, and thus instant JPEG's, if done well), and of course, lower noise. If a sensor allows you to go to at least ISO 1600, and still be (really) clean, then that's very important. If you're very picky, and need enlargements, nothing at a reasonable carry-able size, does a truly clean ISO, over 3200, yet. So what about lens aperture.
The best way to improve all these things, and more, is with a wide aperture lens; that has other good IQ qualities (corner to corner), and some of these can be helped, with instant firmware processing, and that's grand. However, to get F/1.8 or wider, you currently have to limit yourself to prime lenses only, in the main. This is great, when they cost less, but only some (in your system) do. A zoom lens is convenient, and if built-in, keeps dust out of the sensor, but that's not to say changeable lenses are not good too. The problem, with changeable lens systems, is they know you will thrash, through many lens purchases; until you figure out what compromises, you want to make. When it comes to "zoom", I think we'd better better-off using our feet, at least first, before a slow zoom.
Yet, that's the thing. We could use much faster, and smaller zoom lenses, whether built-in, or not. Also, we could use much less expensive primes, that are at least F1.8 at the wide, and good qualities across it's aperture range. While I think Image Stabilization (IS, and best in the lens), is great for slow kit lenses, it's much less important, with truly fast lenses. F2.8 being the middle between fast, and slow apertures. I'm aware that an F4, might be considered fairly fast, when at ultra telephoto focal lengths. So, I think a equivalent focal length around 450mm could best, at under F4.
Keep in mind, my main point is not just one of these better qualities, but all of them, combined, and with a small size, and a more sane price. A smaller size, and somewhat smaller sensor, will allow a much more carry-able telephoto lens, such at the Micro 4/3 tele lenses show now, but they need wider apertures. As you know, a smaller sensor tends to be of lesser IQ quality, but new 4/3rds sensor are getting better. The new G3 from Panasonic demonstrates this, but besides being far over priced, suffers less quality than new APS sized (DX, EOS) sensors, especially at higher ISO's. Now note, while the competition can always make a larger sensor, with it's better quality (all other things being equal), once ISO 3200 becomes super clean (perhaps the next 4/3rd sensor design) it hardly matters, that the larger sensors can do "better". That is, if the camera also has faster, wider aperture, lens choices!
Fast lenses with many good Image qualities.
Sensitive sensor, clean at high ISO.
Full featured body, without missing issues, and in an affordable "system".
All being more manageable, especially in a "system" camera; that requires carrying multiple lenses.
Not to bolster the 4/3rds industry or any manufacturer, in particular (I kinda have the most respect for Nikon), but it's almost there, except for poor JPEGs, too breakable, and a higher cost, for lesser pictures. This needs revision. Nikon, and Canon, need to enter the (about) 4/3rds, systems camera arena, with a better sensitive sensor, and they need to do it, with non-jello video, stereo mic jacks, and quiet lenses, that allow full control shoot vids, or stills.
You know, what an aspiring manufacture could do, is make a system; built around affordable primes, but not with a lesser sensor. This way, the primes would not require and zooming stabilization, or quietness (accept for AF/AE), and utilizing the newer contrast focus speeds, and nicer EVF view finder(critcal to be built-in), and live view, high-res screens, and 1080p capability, compressed. It should include low cost wide, normal, and super-tele (equivalent) primes, and you'd be done; in a smaller bag, at less cost!
What matters most, is the pictures. However, $5000, and carrying bricks, is the wrong direction.
Either make a comprehensive, wide to tele zoom(built-in; for lower cost?); that's fast aperture; mated to a high ISO sensor, or make the 3 affordable, and fast primes, mated also, to a high ISO sensor.
EDIT (in response to mattdm):
No, I do not care for the sensor, in the Nikon 1 system.
MFT should be used for ultra-zoomers. Yet, I would not begrudge anyone playing with manual lenses on MFT bodies. AF just gathers more keepers.
The OM-D E-M5 is a fine camera; more in keeping with what I had envisioned (and kills the GH2, BTW). I just do not like it's lack of focus tracking, and it is not much smaller, than a D40. Newer hybrid contrast/phase AF is the future, along with hybrid viewfinders. I'm still waiting, and overpriced, does not qualify, for me.
I'm shooting D40, and holding-off, on a new body/system, at this time. Take that as my recommendation. When they make something I like better, then I will buy it. The D5100 was a target of mine; but now there's the D5200. I desire a camera I can carry all day, therefore, I am not looking at the D7000, and have also concluded AF-S lens(some affordable) are better, anyway. I have also concluded, that I can not get the shoots, and performance, that I get with the "old" D40, in smaller cameras. The DX system is well made. The D40 is not very large. It does passable low-light, at ISO 1600, and so even better, with lights. While I think a D5200 is overall better, I am not sure, that it is, in all things, and that's not just the overpricing.