I have the HD twins so I can definitely feel you. From what you say and the games you have listed, you seem to mostly play single player games. But the 360 is meant to be a MP console and most MP games if not all are better on it because of party chat, better porting, etc. Plus the exclusives on 360 are also geared heavily towards MP players.
Personally I play all my MP games like COD, Halo, etc on the 360 while the PS3 lets me play JRPGs and other exclusives. So having considered all of these factors, I think you should probably sell your 360 as it is unlikely to serve much purpose to you. Any future exclusives that may come out on it are likely also to be shooter or MP kind of game, so you'll probably not lose out on anything you are interested in.
