Yeah that gamestop pro card thing is actually entirely worth it.
The initial $15 will quickly be earned back with all of the discounts and trade in credits, and you can essentially use it to "rent" used games for free.
And to answer the TC, no, I don't. Whenever I decide to buy a game it is one that I truly want, and I always purchase it brand spanking new. Then again I purchase 1-2 games a month at most on average; I'm not the type that has to play every game ever, even the ones I don't want to, just because. I'd rather whittle away hours on a single game I love than play a variety of crap.