When I hear "is it worth it?", my mind immediately shifts into math mode. From a pure cost to value ratio, yes it is (cost = how much YOU paid for the credit, value = how much the credit covered). However, the caveat is that it is a larger investment (both time and money).
You'd want to make sure that the plan would fit your trip first. Just because it looks inexpensive to upgrade to it, doesn't mean that it'll work right for you. My typical list of key points to make sure it works for you and your party : (stupid emoticon for party made me have to put a space there

)
* Are you ok with spending ~60-90 minutes eating each meal?
* Are you ok with planning out where you'll be ahead of time? While several don't need to be at the full 180 days out, you're not going to want to wing it with DxDDP.
* Are you ok with mostly TS meals? And at those TS meals, mostly 3 courses? For each person in the party?
* Are you ok with the initial outlay of extra money?
It IS a lot of food, but there are some ways to manage it:
* Spread meals out - Since you're getting 3 courses for lunch and dinner, a 12pm lunch and a 6pm dinner may be too close. I like to go to lunch between 11 and 11:30, and save dinner for ~7pm
* Utilize the signatures - They don't give the utmost super-duper most value per credit spent, but they'll average higher than the actual cost of the credit
* Don't be afraid of a few QS - Much like the signatures, not the best cost to value, but other meals will come out much higher and will balance these out. So long as ~75-80% of your total credits are spent at TS, a few QS will not make you fall into the red.
* Skip an entitlement if you need it - Again, losing out on some value, but if you just don't want that app or dessert, don't order it. It's not going to break the plan for you
* Don't sweat a couple unused credits - The plan will likely start coming out ahead around 80%, so if you have 2 or 3 (depending on the length of stay) credits remaining, it's not going to kill you.
Now, except for the first two points above, you aren't going to want to do that for every meal, but they are ways to trim down the raw amount of food that you'd be having.
The last bit would be to sit down and do the math if you're still on the edge. Figure out approximately what you'd order and see if it makes sense.
For an example, with my upcoming trip, I am intending to do the same as you (note that for 1 person @ standard CBR for my dates... it's ~$34 cheaper to use the free dining plan promotion and upgrade to DxDDP than it would be to use the public 25% discount, buy the same tickets, and pay for DxDDP.) I have the following key points: (9 nights)
* 17 ADRs totalling 20 credits used at TS (will be 21 if I can score an early Citrico's or Narcoossee's on my 2nd party night)
* 7 planned QS meals - mostly breakfast, but 1 dinner and 2 lunches in there
* 2 unused credits (will be 1 if the above ADR comes through)
* Saving ~15% - (My estimated cost is ~$972, and if it were OOP it would be ~$1142)
Now, comparing to my math for DDP plans (which would differ), I could save ~$187 by not upgrading, but I'd only save ~$40 on DDP. Upgrading gives me an extra ~$300 worth of food, for about $200. Plus far less OOP at the time of dining (not really savings on that part, it just gets shifted to beforehand).
Of course, I'm also a nerd and I really like to look at all these numbers

I certainly would not expect anyone else to delve that deep.