Given the number of posts on this request, I guess I'm in a small minority but I'd love to see a maximum artwork size option as well.
I use MB (amongst many other things!) to manage an SD card of MP3s for my car's music system and the car's screen won't display any artwork larger than 500x500, which means a tedious manual step for me whenever adding new music.
If there was a dictionary definition of a first world problem, this would be a good candidate but doesn't hurt to ask ;-)