I still have a 1st Generation iPhone because honestly, the iPhone has been the same since the day it came out.
I'm a bit perplexed on this point -- the iPhone has gone through 2 major software revisions and is about to get it's 3rd. The interface has been evolving, not radically changing -- but to say that the iPhone is the same is a bit of a stretch.
I won't disagree that the original iPhone and iPhone 3G were basically the same device, but with a 3G modem and GPS in the 3G. But the 3GS was a massive improvement in CPU power over the original. They also upped the camera resolution and added the compass hardware as well. They also bumped up the max storage from 16GB to 32GB. And going forward, the 3GS is getting multi-tasking while the 3G and original aren't due to their lower amounts of RAM.
If the rumors of the next iPhone all turn out to be true, it should be a very competitive with the Incredible. Front facing camera, flash for the camera on the back, A4 based CPU, double the resolution screen. I would expect to see 802.11n since the iPad has it now -- though they might keep that on the iPad only for now. And we'll probably get some improved battery performance too.
And all of the iPhone 4.0 improvements as well -- the iPhone hasn't been sitting still the past three years.
I can see the Incredible is a viable competitor, but I can't see how the iPhone hasn't been keeping up as well. Either phone should be a great upgrade over your current iPhone. I still prefer the iPhone OS myself, but that's your own call