When the iPhone 3GS came out I was casually thinking about getting a touch. The masses were saying "it's a minor upgrade" even though it was about twice as powerful. I decided to wait a few months until the changes were adopted in the touch, knowing it would greatly increase longevity and support for the device. Ever since, I've been glad I have the more responsive device and now I'm triply happy about waiting.
That being said I'm guessing there's going to be huge hardware development in the next set of releases. I'll be perfectly happy if I can run everything for a couple of years before upgrading again in Sept next year. These things aren't all that expensive to begin with and they fetch a decent price on the used market.