Last trip we upgraded from the free standard plan to the 1Ts 1cs plan. Kept all the receipts and did the maths when we got back.
Saved us several hundred dollars over the two weeks.
Upgrading from a "free" plan will almost always save you money assuming you want to eat at table service restaurants. It's $23 extra to upgrade to the standard plan, and most TS meals are at or above that price. So throw in drinks and dessert and it's almost a no-brainer to upgrade if you got the QS dining for free but also want to eat at some TS restaurants.
Upgrading to DxDP from a "free" plan is $64 a day (or $41 more than upgrading to the standard plan), so if you know you'll be eating at least two TS meals a day, every day, then it's worth it, otherwise probably not.