I think that painting parts of the interior to match the exterior color might be a nice touch on the Elise. Maybe some of shinoo's carbon-fiber seats painted yellow w/ black inserts to add a bit of flair, too!
I've always liked the C4S interior color add ons. Looks great. Due to the size of the Elise I don't think that the seat back would work. However, I'd love to see a crest in the headrest and color stitching. Center console is a must. Hmm, I can just see a CO center console in the middle of all a black interior.
I'm thinking about going with a GG Elise with the red leather (lss, touring, hard top) and it would be pretty wicked if you could find red belts to match the red leather. Or maybe it would look overdone. It would definitely be wicked if you wanted all black leather to add red belts, though.