You know, I actually didn't even remember that we put this in, but it does look like we surface a "logo_size" parameter for teams. ie,
CODE
http://fantasysports.yahooapis.com/fantasy/v2/team/253.l.102614.t.10;logo_size=large
The logos themselves are a bit inconsistent in size, though -- especially for the user-created logos, we're showing the 64x64 version instead of the 96x96 version, and the avatar is an entirely different sizing. So...they're generally larger, but not necessarily better.
...oh, that's a hassle. Okay, we also *sort of* support a size of "96" that generally returns 96x96 logos, except it doesn't work correctly for people using the default logos. I can try to fix that up, just need to see why it's such a strange access pattern for the data.
EDIT: Ha. :PAnd just use the large image if the 96 image isn't available. Quite a bit hacky, but it'll work until we get some of this configuration stuff fixed up.