I think it would be fun, I too have the Fuel mod for Vice city and i like it..
Honestly tho it would be just like real life.. kinda.. before a mission make sure your fill up your car.. I mean cmon lets just pretend we are in this situation:
Get up, get dress, get in your car planing to drive to Ebgames to pick up your copy of GTA 4. You look at your gas tank an its on empty, and you know that ebgames is 20 miles away, and you cant make it on empty. Are you gonna tempt to make it there on empty or would you fill your tank up.
Lol
I personally think it should be an option to either turn it on or turn it off to please everyone..
or ill just buy the PC version to, and wait for a fuel mod
but thats my 2 cents..