By Colette Bennett Mickey D’s new dessert is no apple pie. Dessert might seem like an afterthought for some of us when we pick up fast food for lunch or dinner. But don’t underestimate how much those little add-ons can add up for the major fast-food chains. Wendy’s (WEN) – Get Wendy’s Company Report Frosty, for example, has been served since 1969 with barely any changes beyond price. It was 35 cents in 1969 and today it’s 99 cents, which is still reasonable if you consider how much inflation has boosted our food costs today. Taco Bell’s (YUM) – Get Yum! Brands, Inc. Report cinnamon twists have…