Check out the demo to The Longest Journey for a save/load system that is like the one I described. They use 6 slots per page and features many pages. The thumbnails aren't too difficult to see and those visual cues are very helpful when you've been away from the game for a while.
http://www.longestjourney.com/download/demo/Here's a screen from my own system. It's modeled after TLJ but of course it's nowhere near as slick looking. It's just for placeholder purposes. It also uses your old save/load system and I've added a time/date stamp to it, and it's only limited to 8 slots because of this. Regardless, you can see that the thumbnail is easy to make out. Another technique, in addition to using multiple pages of slots, would be to use a scrollable area. Either way, you wouldn't have to worry about cramming all of the thumbnails on a single screen.