I'm in agreement with just about everything posted here. You shouldn't need a 30 band EQ, but if you don't have a parametric EQ, you may be forced to get a 20-30 band because every car reacts differently and freq boosts and drops can occur anywhere.
Only issue with parametrics is the cost.
SVT Contour, the biggest detriment to a system from an EQ is dial happy users arbitrarily boosting and cuttin freq. The signal chain applies more to home systems then it does to cars because of the much higher ambient noise of a vehicle.
For competition purposes it can mean the difference between first and last, for a non-competition vehicle, it's debatable whether it's necessary.
