Just a thought, and I'm sure it won't happen, but what about the use of hotels/motels as a save point? I hear the camping notion from RDR mentioned a bit through the forums and obviously it's impractical to a) camp in Los Santos and park your car beside your city-campsite and NOT have it stolen (although it would be funny to see your protags reaction when he wakes up to find his car gone or trashed).
A catch would be that you can't go there when you have a wanted level but you could plan your heist there. There'd be a nightly fee attached and maybe valet for the more pricey hotels.