do they do anything besides look good?
They give a little extra shielding from hum. I wouldn't advise removing them however. It's a little tricky, more trouble than its worth. Better off to get new uncovered pickups.
i heard they loosen up the bass a little and warm up your highs, nothing big and not vernoticable. but im not sure.
^A lot of players in the 70's removed the covers and started that myth. If you use an ocilliscope (sp?) you can see the difference but as you said its not very noticable.