Here are a few ideas: Vice City would be great:
-Everything could be set in the 2010 era
-A few new Buildings
-Finished off construction sites
-Updated cars, houses, ect
-Add no extra islands but make that the player can enter nearly every building in VC.
-Make more things to do and see. ie. Player can Fly aircraft again
Vice City can Visit SA:
-Set in 2010
-You begin in Vice city but can also go to the airport and book a airline ticket to SA
-You can play in both Cities, VC & SA
-More choice of cars and guns
-More fun ie. Can date girlfriends again, Pizza Missions, Police/Fire uniforms, ect