A library of dive books for local dives is handy. People will pop in an inevitably end up buying the book anyway
Oh, that's a GREAT idea! A small bookcase with any local guides and critter ID books, and then a supply of the same books available for purchase. If you have problems with them walking off, put chains on them.
Diver friendly hours would be nice, too, although probably not realistic. One of the only things that makes me think about my own compressor is the nuisance value of fills when you have an opportunity to dive for several days in a row. You either can't get to the shop before they close in the evening, or have to wait until noon the next day to pick the tanks UP. (Although I guess the solution is to own more tanks, we already have 14 and STILL run into this trouble!)