I think Apple could do it tastefully, they just have to have moderation, not all black, nor all aqua, nor all white or brushed or whatever.
I think some things look good how they are now (aqua or graphite scrollbars and menu, iTunes sidebar, grey transparency as implemented in iPhoto, iTunes)...some things, not too hot (brushed interfaces, iTunes flat scroll bars).
There is no reason they can't combine this all together in some great looking package, they just need to make it consistent across their apps (or at least have a reasoned and consistent method for inconsistences (i.e. Mail, iCal, Address Book look slightly different from iLife apps, look slightly different from Finder due to functional reasons for differences, not some haphazard mixture).