Well, except for one shelf of recent purchases and "to-reads", mine are sadly all stored away in preparation for a hoped-for move. But even before several months back, the really old stuff has in large plastic tubs out in the storage area.
But now I'm dreaming... can you imaging something like one of those motorized multi-shelf units what see sometimes, especially at a multi-practitioner Doctor's office? Where your shelves go up (or down) and then to the back with the easy touch of a button.
Or better yet, go for the really big office, where the large shelves are on tracks and roll right next to each other. You pull apart the shelves (I'd say motorized there too, but maybe this way you can get your workout at the same time you are pursuing your "fun" focus) until you get to the one you want and have walking space in between them to actually access the book you want/need.
Shoot, just buy an old dry-cleaners warehouse. Now you can put a small box/semi-enclosed shelf on each hanger and push the button to speed around to the collection you want.
Ok ok, not really practical, but fun to imagine!