Gas idea is great.
they should mix other games in with gta4 and make it the ultimate gaming franchise
even if they price it at $5000 as long as they mix in other games with it.
Metal gear :
a UPS truck driving down your block and dropping boxes with people hidden in it popping up and shooting you with silenced socom rifles.
Counterstrike/Cod4/Madden :
Planting a bomb at your rival gangs base and having local gang members call the police or
the SaS where you are able to play too, COD4 first person style.
Planting the bomb should be done madden style
Running down city streets with bomb in hand.
breaking through gang members
Assassins Creed :
Having people disguised as bums/crackheads/whores/ infiltrating your gang base and assassinating your gang leader.
Skate :
You should be able to skate around the environment and perform tricks like ollie kickflip etc. and yes you can also have your skateboard jacked
Red Alert :
You should be able to defend your base and have the ability to build tesla coils around and also guard towers
You should be able to destroy your rival gangs source of food and water, like shutting down pizza places, fastfood, restaurants near ur gang base.
Where they will get hungry and thirsty and look for food n water, man vs wild style..
which would result in them dropping down in sewers drinking sewer water bcoz they're so thirsty..
this is where ninja turtles can ambush them and you get to fight them off with your chainsaw or your katana or your pistol. Ninja gaiden/ Devil may cry third person style.,
injecting their food with T-virus is a good idea too and having them turn into zombies
Ace Combat :
You can also play airplanes/helicopters ace combat style.. you can do dogfights, or you can also parachute gang members down to rival gang base.. OR..
Spiderman :
You can play as spiderman and shoot cobwebs at enemy helicopters and airplanes n shit.
The pimping hoes idea is pretty good, but you should be able to spend money on your hoes like give them breast implants,nose implants etc, where your able to adjust there size via fight night creater mode style, with tha analog stick
the better they look the better they sell
Car Radio :
The car radio should be tweaked and also if you made enough money you should be able to add a dvd player to your car where you can watch movies while your friend drives n shit.. puliing drive-bys while watching menace 2 society would be tight.