It can be really hard to take stuff up to the attic when you still like it, but it usually ends up looking best that way. What I'll do is pick one surface, like my dresser, and take everything off it and set it all on my bed, then carefully put some pieces I love the most back, rearranging them, stepping back to look, "hmm"ing, and calling family members in for second opinions until I get it just so. Then I usually still have a bunch of crap on my bed. I might then move to a different area, like shelves, and some stuff from the dresser might go there, or I might just call it a day. But anything that's on my bed at the end has to go upstairs. Getting it out of sight for a few months makes it more special and new when you bring it back down, anyway.

Oh, purple is definitely an easy color to come by come dorm shopping season! White, too. And everything is usually quite modern, so I'm sure you'll have no trouble finding some pieces that'll spruce things up then.