Nothing TOO realistic should be included in GTA4, because if it was realistic, every crash would be lethal, and that wouldn't be any fun.
Elaborating on Xenon's idea:
Another idea is lockpicking. When you go to a car, if it's locked, you take a few seconds to lockpick it (and possibly get caught by the cops), or get a bat and smash the window.
But that could make it too stupid, if cops keep arresting you.
There should be opening doors for more interiors, and NO SIM LIKE FEATURES.
Hunger is stupid.