I'm way too cheap to pay $10/yr for a forum so it won't affect me. It took me years to break down and pay for SA and that is $10 until you get banned. I'm not quite used to car forums and their strange rules yet either.
Honestly I don't see any incentive for buying premium aside from the sticker.
I DO like that the forum is relatively add-free and I suppose that is one potential bonus for me.