I know I'm gonna sound like a party pooper, but I'd probably be ready to go in 7-9 days. On our last trip, I actually found myself not feeling the magic very much, and getting a little bored. I don't know if it's because we were there for that long, or because we were there without our son, or if it's just because we've gone almost every year since being married...or possibly because this is the first time that we've done partial days in the parks, coming back to the resort midday for breaks, whereas I'm used to being there from open to close. So I'm not sure exactly why, but for some reason, I was feeling less magic than in previous trips.
Regardless, we wouldn't be there for 2 weeks. On our off property trips, we were there 10 or 11 days, had a blast and then were ready to go home at the appointed time. And after staying 8 days this past time, we were both ready to go then, too. So my ideal trip, no matter how much time or money we had available, probably wouldn't be much longer than 8 days. Possibly 9 or 10, but not any longer than that.