Three things. First, be sure that you're comparing like rooms for that extra $200/night. Often, concierge rooms are in better locations and views than standard, so that can account for some of the extra cost. You may be moving to a view room from a standard.
Second, you have 5 people in your party. Don't underestimate the savings involved with having "free" food, snacks, and beverages, plus a lounge to relax in. The cost of those in the parks is very steep! Water alone is quite expensive (unless you use the free water). $40/day per person seems like a lot, but it adds up very quickly. When we do concierge, we make lunches out of the bagels, cheese, cold cuts, and fruit. There are Uncrustables and desserts and so on.
Third, if you're staying at DLH, it's very convenient and nice to go back to the hotel on the monorail and take breaks. The lounge has a nice espresso/cappucino machine, a snack time with homemade chips and salsa, desserts, beer, wine, and liqueurs all day, etc etc. There is an evening hot appetizer and honestly, you can feed your family quite well on the offerings in the lounge. You may normally stay in the parks all day until closing, but when you have the lounge available, you might find it a nice change to take breaks.
I love being able to get up and head straight to the lounge for my coffee and breakfast before heading to the parks.
It's still a stretch to say it's worth it if you're only figuring it in dollar value, but we love it when we can swing it and find it worthwhile for our family of 5.
ETA: Did I mention you get all the free beer/wine you want?
