We also do the deluxe dining plan. It really depends on how many people in your party, and where/how you'll be using your dining plan points.
Quick service meals don't require a tip. Unless things have changed in the last year and a half, I don't recall there even being tip jars at the counter-service restaurants...
Sit-down dinners, you should plan to tip based on the value of your meal - so if you'd normally tip 20%, and your dinner for two at Le Cellier would have cost $120 out of pocket, you're looking at a $24 tip for that one meal. Buffets come in for a slightly lower % tip, usually, but again, should be tipped based on what the meal would have cost out of pocket.
If most of your planned meals will be at the table service restaurants, well, if you want to do a little math, you can estimate the possible costs of your meals and then have a rough idea of what your tip budget should be...