For stopping the respawning when towed - if in x radius of impound lot, it cannot be respawned. And I agree on a respawn timer.
I cant lua so forgive me but is it a Hook? ok
If we can make a hook to know when a car is being towed we can stop a car being respawned whilst being towed, then we can go into what BLT said and put a radius around the car inpound lot disallowing a car to be respawned, if a player tries to respawn their vehicle they can recieve a hint saying
"Your vehicle is currently being towed or is at the impound lot."
Another suggestion would be having a hint read out to the owner of a car saying that their car is being towed and not to respawn it or run the risk of being kicked/banned.