I actually got to the same point you did on my 5th playthrough literally two days ago. After getting all the GF's, cards, optimized junctions, and getting all the way through Lunatic Pandora before facing Seifer and thus preventing me from going back at all, I just quit; there was nothing left to do.

That's the problem with FFVIII: in 70 hours of gameplay on that file, there was absolutely nothing else rewarding to do that wasn't incredibly tedious or downright boring. Hope you think of something because I sure as hell can't.