I want to share some small ideas with you, so I'll go on. 1. Quest System
They are quests that appear daily and give just a small reward and would be repeatable on the next day.
Quests, which reset every week and are harder to finish and therefore be given a higher reward.
They are the next step based on the daily and weekly quests and obviously take longer.
It can take up to however long, depending on how consistent one player is, and this could lead a player to be more active than ever, putting up a huge reward in the end of the tunnel.
2. New (adding) achievements, like ...
Complete a randomly named map!
Complete a map by doing a doubled backflip!
Die 100 times!
Drive for at least 10 seconds on 2 whells!
Take 10 different vehicle changes!
Activate Nitro 50 times!
Collect 150 Repairs!
Win 3 maps in a row!
... and much more!
3. Recruitment System (recruit friends to play in our server)
Well, let me explain shortly what Recruitment system represents. Rewards are only awarded in the game where the initial recruitment took place. If someone recruits 5 players to the server and they are playing actively he will get reward like money or something else of your choice. For these who use fake system and trying to avoid the rules he will be banned for a certain time or his stats will be resetted.
4. Server events
Organising in-game events like Player of the month would be great idea. That event can be played by all server players and there will be system which shows player points. Duration of the event will be 30 minutes and first player with more points will get rewards like getting forum status Player of the month or special tag for him in-game. Points will be earned only if you kill somebody otherwise you won't earn any points. This event will be played once in a month.
I really like the second one, because it would be a bit funny, if we get some new achievements, like those.