Interesting thread, but I noticed a couple of things that are important to point out as I'm sure many people who are reading this thread are grappling with whether to do the DP or DDE, and so they may use this thread to help in that important decision:
1) Lots of sharing of meals, but most people can't get away with that.
2) Tips do seem low. Although tipping is personal, when factoring in savings for
DDP or DDE, tips need to be included as it reflects the total cost of eating. Again, just like with sharing meals, low tipping will save money. (It's already included in DP).
3) Didn't mention ages of children, until I saw DD1 - 1 year old babies don't each much (my daughter breastfed until 14 months, so at 1yr. old, she didn't eat much at all). Another cost saving measure.
4) Food choices are all quick service or fast food - cheapest dining choices on property. For breakfast in room, did you add the cost of those foods to your budget as well?
Based on the OPs budget and family needs, she is happy with their dining experiences, but in all honestly, the above mentioned factors will save money for all families, especially when sharing meals. Since many families are struggling with whether to do the DP or purchasing DDE, I think it's important that people look at the ways that the OP saved money. Sure, she proved that a family of 4 can eat for approx. $75.00 per day, but it's with an infant, sharing meals, eating fast food, and tipping low. Not judging the OP's choices to do this, but I know that this system wouldn't work for many people and so if people are reading this thread it might give them false hope that they don't need to do the DP, when in fact there are a lot of uncommon variables in the OP's situation that can't be applied across the board for many families.
For us, we only eat table service restaurants as we eat well at home and do so on vacation - no fast food for us! For my hubby, DD3 and myself, the DP is costing us $87.00 per day. We will be eating: prime rib, chicken, soup, fish, pasta, salads, appetizers, wraps, soups, fruit cups, toast, etc. OP would have spent the exact same amount as us as infant is free - so for an extra $11.00 per day you wouldn't have had to share meals, skip meals, etc.
Just thought it was important for me to mention this as every other post is whether or not people should get the DP, and this post proves that it is definitely worth it for most families and would have been well worth it for the OP, and in fact, would have been a cheaper option as she still ate breakfast in room sometimes, and shared every meal.
Tiger
Anyway my point is that once I started a budget without the plan, I noticed how much easier it was with the plan...often we could stretch credits for bkfst and snacks and bring food back to our room for later. 
