There's little I can say that won't be hypocritical, given I had (have) a perfectly usable istDS which I've supplanted a mere 2 years later with a K10D. What made me buy a new body when the old one still worked? Was it the shake reduction? the 4 extra megapixels? Dual control dials? sensor self-cleaning? 3.3fps sustained shooting speed? weather sealing? ISO100? Availability of battery grip? the fact that I had some spare $$ lying around and the Aussie Dollar was particularly good against the USD at the same time as the camera dropped in price? Or a combination of all of them? Don't know, but I bought it and I love it. Has it made me a better photographer? Not sure you could say that.
Lenses - slightly different story. I don't generally go all ga-ga over newer, faster lenses. I'm more about coverage than replacing a fast lens with a slightly faster one. I've got my wide-angle, my zoom, my portrait, my prime and my macro and a couple of kit lenses. I'd consider replacing the zoom, but it would require a fair few $$ burning a hole in my wallet before I'd go there, I think. If I need to get closer, I'll get closer. If I don't have enough reach, I'll take the shot and crop it and if it's blurred I'll tell myself to remember to do better next time.
Anywa, I think that there's three aspects to photography : artistry, equipment, and subject matter.
Equipment is really the only one you can throw money at, so many people looking to "improve" their photography seem to gravitate to that one (and I'm not saying that in a judgemental way - I was taking a portrait-style photo of a teddy bear using a desklamp and wide-angle lens last week, and realising how much easier this would be with a proper lighting rig that would allow me to get further back... and portrait-style shooting with a 10-20 is somewhat sub-optimal anyway.). And to be sure, vibration reduction, sensor cleaning and better handling of noise are all good things. So if you can afford it, why not?
But I agree with you - all these things can be overcome by a skilled photographer who knows his or her equipment and has a good read on the conditions and knows what sort of outcome they want.
Yet as for 'artistry', like I said that can't really be taught. You have to go out there and shoot, find stuff that you respond to, and put that into your photos. Yes, I'm 'proud' of my camera, but only insofar as it provides me with photos I can be proud of.
(All that said, there's still an emotional thing, too, about your equipment. No matter how rational I may be, will I feel a small bit of sadness when Pentax releases a new K10D replacement or a full pro SLR and my K10D is no longer top-of-the-line for the brand? I hope not, and I certainly shouldn't. But I can't guarantee it, either.)
I'm with you on the 'go out there and take photos' thing. I've got a trip to an aquarium planned AND the Lunar Eclipse to shoot afterwards, today after work.
So I'm living the dream