Until babies #2 and #3 came along and the thought of all five of us in one room sounded like the Least Magical Vacation on Earth, and I couldn't handle the thought of paying for TWO Deluxe rooms!
We were there over Thanksgiving this past year (Formosa Gardens), and we had NO problems with closures. We would get there at the opening, hit the big attractions each morning, eat lunch and bail when the kids started hitting the wall and/or it started getting crowded. In general, it would take us a half hour from the time we decided to leave a park to be back in our house. About the same amount of time it would take to wait for a resort bus, ride the resort bus, walk to the building or a long hallway and get back to a room.
It was great to put the kids in their rooms, let them nap and go sit by the pool, hang out and watch TV or relax in our own room. I can never go back to being silent during nap time after that!
After resting, we would go back to WDW and visit another park for atmosphere and shopping. If an attraction had a short line, we'd ride it. We were so relaxed and happy the whole time and I think it was because we were all well-rested and since we had our own room, my husband and I could "relate"
We would do a countdown from 10-1 each day as we rode under the "Walt Disney World" sign and my kids were thrilled to do it each day. On the last day one of my sons said that was one of his happiest memories of the trip.
With the way we eat as a family, I have figured out that the
DDP wouldn't make sense, plus my kids liked getting up early and not having to wait for Mama to put her makeup on before she took them down for breakfast. And I liked having my coffee downstairs waiting for me each day.
We agreed that we didn't feel like our experience was less magical because we stayed offsite, in fact, we thought it was our best trip ever! I don't think I will ever be able to stay onsite with the kids again
HTH you present your case (if sex and saving money doesn't get him, I don't know what will

). He won't know unless you give it a shot!!