Yes, i fully agree on more cars, mods, new vehicle types (snowmobile, jetski etc), but what I REALLY want is a decent garage to store these in. I mean, whats the point of collecting every decent car in the game, modding it, only to find there is no where to store your lovely collection. Personally, I think that you should be able to buy a BIG hotel and like in San Andreas, it should have a HUGE multistory carpark, allowing you to store hundreds of cars in it. Also a shed on the water for storing boats, and a bigger hanger than SA for storing aircraft.
Also, how about boat and aircraft mods... like being able to boost thier power and customizing color n' stuff on them.