System upgrades don't make sense unless you are creating a new console. After all, game designers couldn't optimize their games to the improved hardware because then the older systems wouldn't be able to handle it. As for cross-platform, that's a novel ideal but in practice, I don't think the payoff is worth it right now.
Say what you will, Microsoft has a great console and the Kinect is a novel new idea that sounds really fun to me, my wife, and my kids. I love hardcore games as much as the next guy, but I have a Wii too for the silly ones as well. My PS3 is not much more than a glorified Blue-Ray player, so all the *real* gaming is done on the 360.
While I agree that some sort of incentive for past owners is a good idea, I suppose you could just as easily go to a game shop and trade in your old hardware for a few bucks towards a new console or package.
I lost my train of thought, sorry about the babbling!