When we only had enough points for 5 days in a studio or 1BR (and only had 2 kids) we ONLY went to WDW parks.
Recently we added on more points and have stayed longer. We love to go to Sea World for a day then back to WDW for dinner. Two years ago we went to Universal for 2 days - before we checked into BWV. My teens, however, didn't love it there. So we won't be going back anytime soon.
But what really happened with the longer stays is that we just take it easier. No more marathon days in one park or between two parks. We go to a park at 9 or 10am (can't get those teens up before 8am), stay till 2/3pm, go back to our
DVC room and swim, change for dinner and then usually go to Epcot for dinner and Illuminations or elsewhere.
You can add minature golf....a day at a water park.....Disney Quest for that one rainy day, etc.
We are just more relaxed when we aren't in a frenzy to do everything. And since we've been so many times as a family - we don't have to "do everything" anymore. We do our favorites and try any new attractions.
We actually really,really enjoy our visits. Unlike my friends who come home and say they are exhausted because they are trying to make every second count....we come back fairly rested. That's what a vacation is supposed to be!
We've also added on a short trip to Vero Beach and have considered a side trip to Cape Canaveral as well. This trip we're going in and out of Tampa (cheaper airfare and convenient airport) and may do something out there instead of an additional day in the park. I love the flexibility of longer trips.