It depends. MWeston made a comment yesterday or the day before that for the 100 hours battery life you'd be using a minimalist player that had nothing to do with Linux (Linux, in fact, sounded like it got suspended whilst using that micro-minimalist mode, in order to allow the main ram to be powered down).
Personally, I would be surprised to see visualisations in such a player, if I've understood it correctly.
However, I do see visualisations as being potentially useful - for instance, if you're using Pandora as a cheap DJ device and you have a projector to hand. Yes, of course, the results don't look quite professional... but I've seen bars and clubs (albeit in Peru and Nepal) using Winamp's visualiser for lightshows, and they looked good enough, certainly.
Importantly, though, the interaction between a non-minimalist Linux-based MP3 player that does fancy things with the screen and can use TV-out, and a minimalist 64k or less player where every byte is important might well be complex, if not impossible. So if you want the minimal MP3 player to have visualisations in it, I'd guess you wouldn't get the 100 hours, even with the lid closed and the screen turned off...
Disclaimer: I am not a coder. If the MP3 player + interface + screen drivers + video out drivers all fit into 64kb, then of course, I am wrong; as a non-coder I'm guessing it wouldn't, but as I say, I could be in error...