Regarding Marvel v Capcom 2, the Dreamcast version is good but the XBOX version is better. The PS2 version of the game is not fantastic; the Dreamcast & XBOX versions are the ones to own.

A Saturn is definitly worth owning. The Capcom fighters are way better on Saturn over PS1.
I could understand some reasons 2D fighting games do better on Dreamcast & Saturn..but...The original XBOX version?? I wonder what makes it better on XBOX? Is it because of the XBOX's hard drive? I've seen the reviews for that version and it was lower than the other versions (TBH I never played MvC2 on the original XBOX myself so I don't really have an opinion of it, even though I use to own the console like 10 years ago but I only owned the crappy titles on there).

I've read in the past that there are resolution issues with some of the ports on say Dreamcast or PS2. iirc the Saturn has a closer or identical (?) screen resolution to the Capcom arcade version. Whereas the Deamcast graphics are redrawn or stretched or compressed or something.
You'll have to do some more research to find out the details on that issue, it's certainly been discussed repeatedly in many forums over the years. Or maybe we'll get lucky and someone here knows more about it.
How about when you try to put your TV in 4:3? Does it still make the game look the same??