The 360 has been running on all cyclinders lately. The recent releases have been top notch. I would hold on to your system because trying to get something back once you had it sucks.
I'm curious with all the recent great releases nothing has stoked your interest? Too be honest I played the wii and although I love nintendo I wouldn't trade in the 360 for the wii. I played the off road game and I really believe that they could have don't that on the gamecube. Only the controller was different. Plus you want to see if the wii get REAL 3rd party support post launch.
Trade in the games you don't like but keep the systems. I believe the 360 will be the front runner after the hype and fanboysget there ps3 Nintendo will get theres. Another question to ask yourself do you get caught up in the hype of a game release? I see a whole lot of games coming down the pipe you might want.
I had a small period when my system was idle then the games started coming in combined with live....play on Good luck.