Id love to see houses having way more use than just storage, and i'm in complete agreement with ripply, the economy needs to be a lot more realistic.
When you get your first vehicle it should feel like an achievement, but right now it doesn't, When you get a house it should feel like a Huge achievement and make you so happy you jump up and down like you are a little kid watching spider man or something, I have always wanted each and every house to have their own garages with a car storage of 1 or 2 vehicles, this would make logging off at your house more realistic and then when you get in the server you wouldn't have to steal a car, every time you logged in at your house
the black market should be for everything illegal not just guns, illegal vehicle modification (like reinforced glass for example) weapon's and weapon modifications, body Armour etc. and the black market should be a market as well, where you could sell illegal goods like an shop you sell the goods for how ever much you would like to sell it for, and then you could get gangs involved and they could have decreased prices on goods and then can sell them back to the player for cheaper than what the base price is but more than what they bought it for so they turn a profit, and like muffs was saying drugs should have advantages if you use them (which would give players a reason to buy them).
there should be reasons to use boats, turtle catching for example would have to be fished in certain areas in the sea, lets say 4 certain areas, you could either net fish for the turtles, you could jump off your boat and go spear fishing (no idea how that could work) and you would need lets say a scuba gear set, that you could get from a job or you could make it where that gear is illegal and needs to be bought off the Black market. another way to make boats more useful is let people catch an expensive fish if they are lucky so you are fishing for an hour and lets say you catch 10 salmon, and a bunch of other fish, the salmon is worth a lot more money than the normal fish you would catch, in our economy it would be like 5,000$ or what ever per fish but the chance on catching said fish balances it it would need to be like a 1-5% chance on catching it etc.
Planes should be allowed to fly over the city ( i have no idea why that is a rule ) and planes should be more useful to players, helicopter rides should be able to be bought from airlines, they could assist you with reconning a bank robbery location, and possibly get you up to a area you cannot get to without a helicopter, they could be bought off, or you could just go for a cool helicopter ride (I understand that airlines would every now and then give plane rides) there should be a advantage in flight, maybe you add tole roads between the city and the county, so every time you would cross the road it would cost you like 500$ or what ever amount is reasonable, and make the price for a plane ride to the airport 50-70% lower than those roads (you could make it so the speed cameras are in a certain spot on that road and it costs you how ever much when you cross it, regardless of speed.
The actual bank on vine wood should be robbable , I understand voice range is a big problem so you could have a few guys up to the front so they can talk to the officers outside, there could be security officers posted outside (securo serv boys) for added role play, and it would require a group of people to actual plan a robbery on the place, the way you could make the Securo serv guys guard the place is like the bank job, make them go there and have it so they gotta sit there for like 10 mins to get paid and have it rotate thru a few locations, and make the pay good. Additionally regarding the voice range, you aren't required to be able to talk to the dudes inside the bank, yea it would be nice to talk to them but it doesn't always work out like that, you can try to but if you get no answer you are going to have to make entry on both entrances, also regarding the vault door issue, i'm sure members of the dev team can figure out a way to either make that door static and unopenable, or remove it
im just spitting what i got in my mind out there, i want to see the server become the best it can possibly be, some of this might be a little unreadable but im sure you managed.