I hope that you guys aren't aware of this yet, but I was playing the PSP version of MUA2 this week and I noticed that they reused Wyatt Wingfoots model for a rebel mutant in that game.
https://www.youtube.com/watch?v=9Rev-P8CZgE (https://www.youtube.com/watch?v=9Rev-P8CZgE)
Considering how evidently low the budgets for the last-gen versions of MUA2 were, it doesn't surprise me that they would try to cut down on costs by blatantly reusing a ton of assets from the first game. Heck, when characters jump, the grunts for the MUA1 voice actors still play in spite of hiring new actors to voice many of them!
But I suppose to Activision, it only served as a means for some quick cash from stragglers who still hadn't jumped ship to the newer consoles of the time.
You'll find that in a lot of the content. X-Men Legends II reuses a lot of models from X-Men Legends, and the PS2 version of Ultimate Alliance shares a few models with them as well. In addition, certain models are reused or slightly modified for different characters. You can see this in Jean Grey's Phoenix outfit (which has been present in all 3 games since X-Men Legends) and Medusa's model. They're almost entirely the same, except for the fact that Medusa doesn't have the belt. Medusa even has a small section on her upper chest that isn't quite symmetrical, which is where they removed the Phoenix logo.