Mod a case if you don't have a PC for it yet? I just bought a case with PSU at the garage sale for 3 Bucks
The Vectra 286 was another 2 bucks... thats irrelevant.
Anyway would it make sense for me to start modding this case even though I don't have a rig to put inside?
You could paint it, and do som eother stuff to it. I don't see why not. The only thing that might be hard to do is cut holes for power cables, but most power cables are relatively in the same spot on most modern boards.
Actually, it makes MORE sense to mod a case you don't have a pc for yet... that way you don't have a bunch of components just sitting around depreciating while you mod. Of course, that depends on how much you plan to do and how much free time you have to do it...