Sounds groovy to me too.
For maximum chances of finding some art (often, even a tiny image is better than nothing at all), I would allow all art to be uploaded, and have the app intelligently choose the biggest one for you when batch downloading.
Keeping the "loose search" feature would be good too.
I know that when I've shown MC to people, they've been impressed by the way you can navigate by art, but then put off when they found out how difficult it was to aquire that art themselves. This one step process would be a killer feature for most people I think.
I've spent a long time, using MC, Sparta's plugin, and Google images to get all my art. Just over 500 albums have art at or above 500x500px. Another 500 or so at about 300x300px. And another 400 at smaller than 300x300px.
Happy to upload it of course.