Although I agree that too big would be dull and possibly repetative (just look at LA in TC:SoLA), I thought SA was reasonable. It only takes 2-3 minutes for most long journeys. Gives you a chance to listen to the radio, which I love doing.
If you look at VC and compare it's amount of gameplay to the map size, then do the same for SA, the ratio is quite different. I don't know exact numbers but from experience the SA map is about 4-6 times bigger than VC but the game a bit under twice as long, meaning less game per square inch (if you will). If they keep the ratio closer to what is was for VC I would imagine this would help.