sell the old consoles as well, and the games for them. One thing I've noticed is that GameStop and EB never seem to have a NES or SNES in stock, and I've been looking for some for quite a while (I don't trust eBay too much).
If I bought a SNES from you, and you had a decent-sized rack of old SNES games for a good price, I'd most definitely come back.
And if you don't want to use floor space for old games, you could do what a Funcoland near me did before they were driven out of business--keep all the old games out back, and have a print-out (Funco's was actually printed on what seemed to be newspaper) of all the games you have in stock and their price on the counter.
Imports are also good, and not just for games--look into acessories and even toys to have available.
I seriously wish there was a store like this near me... :(