I traded a Mustang 1 V1 for a Mustang II V2, and I kind of regret it. One reason for getting the II was because I wanted to be able to practice bass, hence the 12" speaker. But I'm probably going to pick up a used M I V1. I can't say anything about the M II V1 (or the M I V2 for that matter), but the M II V2 sounds stiffer, which could be the speaker, and it could be the redesign to eliminate the Fizz that plagued the M III and above. The old M I sounded really sweet and full. If your M II V1 sounds thick and mellow, keep it, especially at that price.
The 12" speaker does work better with bass. The additional stuff in the V2 firmware is pretty redundant, unless you need a "smart" pitch shifter. I didn't think the additional amp models really added much, and the effects, well ... Ah, yes, there is one cool thing: the null model, just a preamp. But someone somehow uploaded an empty preset for the V1 that does it. You can download it via FUSE. Be sure to get into FUSE, these amps don't come into their own until you realize what you can do with FUSE.
thanks for the help!!!
I am not much interested in fx, of course i wanted to play voodoo child and no wah. recomendations?