This may seem like a boring suggestion but it will improve playabillity and lag.

When the server dies down after lots of players there seems to be alot of vacant cars from players who have left. This can be fixed by implementing a 15 minute despawn from when they leave the server. This is also the same for random entities being spawned in on the map i have seen lots of scrap plastic being discarded on the ground and pots if this can also have a 15 minute limit after disconnecting it would improve lag and the capacity to handle lots of players. When entities are despawned they should be collected in storage bank to be reclaimed but there should also be a limit on the amount of stuff collected and a place to easily discard unwanted items.

another thing should be the option to discard items in your inventory, it may seem realistic to put rubbish in bins on the map but it just wont be used because people dont want to do that and will not use it.

If you really want to make a premium/donator membership to the server appealing limit the amount of things people can spawn in like cars pot plants and make it bigger for donators.