Like most people are saying I think there should be more than in IV but not as many in San Andreas, that amount would be pretty useless, apart from for the extra storage for vehicles. I just think that we should be able to earn a nice mansion or a bigger safehouse at the end of the game, much like with Madd Dogg's mansion in SA, it sticks to the whole rags to riches element.
Although it would be pretty cool to have multiple cities, like San Diego. I think maybe just Los Santos would be suffice, when thinking about LA in real life, it is such a huge city, and personally I'd rather they got as much of it in as possible, as realistically and accurately as possible, while including the surrounding countryside. LA itself is a very diverse city, from the beaches, to the mountains, to the cities and the suburbs, I just hope they get it right, which knowing R*, they will.