The issue of "Will I save money?" is a tough one, and it's gotten tougher over the past few years as the prices of the plans have outpaced the pricing of the actual food along with changes to the plans that reduced the value overall.
There are a couple key things to keep in mind that do help gain value from the plan:
1) Stick to higher end TS locations. Overall, with higher menu prices, it'll be a touch easier to come out ahead, even if you're not ordering from the top end of the menu.
2) Avoid 2 credit locations (while paying on the plan). While some of these will work and you'd come out close, it's pretty tricky to make these come out ahead while on the DDP (DxDDP is a different story). If you feel you must, then 1 isn't going to kill all the value, so long as your stay is long enough to make up the difference at other locations.
3) Focus on dinners. Dinners are traditionally more pricey than earlier meals. Not in all cases, but as a general trend.
4) Do the math. I can't repeat this enough. It's all about the numbers. You can check the link posted above, AllEars.net, or even the menus on the Disney site itself to get an idea of the prices for both TS and QS (I use a combination of all 3 myself). Figure out roughly what you'd prefer to order (without taking price into account, one way or the other) and see what you come out to. If DDP is higher cost, check to see if adding any additional stuff that's covered will be worth the difference (e.g. if you normally don't get desserts, but you kinda want them, it may be worthwhile to get them with DDP if the prices are close enough).
5) Ask questions

and don't be afraid to admit when a plan isn't right for you. We get a lot of people here who are stuck one way or the other. Always getting a plan or never getting a plan. The trick is to recognize when a plan works right for your trip (typically, when you're saving money

) and when it won't. Either way, so long as you figure out what's best for your trip and traveling party, then it's the right choice! (Don't let the DDP haters or DDP fanatics sway you! (A friendly note to my DDP hater and DDP fanatic friends, all in good fun

)).
6) I really should be working, but with my trip less than 2 weeks out, I can't focus too well. I think I kinda lost my train of thought here...