Problem regarding detecting whether hacks were used or not has a simple solution...
Storing data of players which will tell you if the player bought bulletproof service or not... And yes, big majority of the car hackers increase their HP to 800...
It will be one more thing to spend money with - money becomes more relevant, you will worry less with deathmatchers blowing you up and will be very handy for convoys, and will encourage people to earn more money and there won't be any more of rich players who have a thousand grands of cash stuck in their bank accounts...