I would venture to say for most people who owned an NES back in the day, Punch-Out! is probably one of their top 10 favorite games for it. Say Punch-Out! to just about anyone who had an NES back in the day and they will smile.
The time is right for Punch-Out! to come back now with the Wii's huge userbase, the casual friendly controls (old school style for those who want that), and the whole "retro-cool" thing going on right now.
New Super Mario Bros. cashed in big time IMO in large part due to nostalgia.