The DP has evolved over the years. Years ago, when I shunned the free Fall DP and only paid OOP, I received incredible service. But in the past few years, servers have treated me better when I have been on the DP then when paying OOP. With the DP, I usually order the highest $ menu items to max the value of the pre-payed plan so upping their suggested tipping percentage. When paying OOP, I often order the less $ items so lower percentage suggested tip for servers. This reflects the value of the DP for WDW guests. Years ago, the DP included tips & 3 course meals. Now, it offers a more minimalistic value and you pay your tips. In the end, it is the relationship you and your server strike up between you. If either you (or your server) or both, are distant and uninterested, then not much will be going on. If you have a good dining experience, it should be reflected in your tip.