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Your car loan is currently at ~88% utilization. I saw a small increase when I got my student loan utilization down below 80%. So while, in general, I agree with the other posters that installment utilization is not too important it can have an effect (small).
I doubt you will get 18 pts but you will likely get a few when your %utilization drops below 85 or 80%.
Opting out on existing credit cards? or opting out on receiving cc offers??? There is a big difference.
Opting out on existing credit cards that give u the ultimatum of accepting the increase or closing the card is bad.
Opting out of receiving offers (which I have done) won't do anything.
Also, I agree that paying down the loan won't do much of anything.
Good Luck!