While sticking with a particular store because of a free loyalty card isn't a very thrifty decision, paying for an additional discount at the same location is akin to throwing away money.
You're almost certainly never going to make a dime off that investment, as the around-$20 price tag generally nets you an additional 10 percent discount. Therefore, if you pay for the discount program at a chain bookstore, you'll only save an additional $2 on a $20 book, meaning you're going to have to flip $200 in the next year on literature to make your $20 back. Sure, the store will offer incentives like special coupons and additional discounts on best-selling titles, but chances are you could find those books for the same or a lower price at a competing store or online retailer.
Of course, if you annually drop big Benjamins at that one chain, the membership may be worth your investment. Our advice? Consider applying for a library card. Libraries have a selection that rivals bookstores, and you can take those very same books home for free, which is the best discount ever.