If I were going by myself, I would definitely do the dining plan. Not necessarily because of the big savings (I'm a vegetarian, and therefore always eat the cheapest thing on the menu), but because everything would be prepaid, including tax and tip, and I wouldn't be able to skip appetizers or desserts because I'm too full/don't need it/costs too much. I would look at it as a sort of "forced indulgence" instead of my usual "try not to spend any more money" mentality.
But this rationale only works if you would do one TS meal every day, and if you don't do a lot of 2 credit meals. If so, I highly recommend giving the dining plan a chance. We found it really added an extra level of relaxation and fun to our vacation.
Edited to add: We must have been posting at the same time. I know what you mean about not wanting to make reservations. You'll be able to get in somewhere, but the question is, will it be where you want to go? We made 12 reservations for a 10 night trip. We ended up cancelling 3 and adding one new one during the trip. I'd recommend having reservations in place every day as a sort of insurance, but don't feel locked into them. You can always cancel if you find someplace else you'd rather go (once you know you can get in). Just keep that WDW dining number on your cell phone speed dial!