We're DVC members, and we do have reservations for the treehouse villas. On the one hand, I always wanted to stay at the old treehouse villas, so I'm really looking forward to staying there. On the other hand, I'd also like to be "closer to the action" so I do have requests for other resorts were they to open up.
While it's great to have something on-property that could accommodate up to 9 people, those prices are pretty steep. I'm guessing it's partly because there are so few treehouses, they can put a premium on them, and they are unique lodging at the world.
But also, consider the cons.
They are part of the Saratoga Springs resort, so you have access to their amenities, but the person I booked with over the phone made it clear that it's not much of a walking distance. You will have to make use of the internal shuttle that goes between the treehouses and the Springs section of Saratoga, OR you'll need your own car.
There is a separate pool for the Treehouse guests (and of course you can use the main pool, but you do have to take the bus to get to it or enjoy a very long walk). It's not an elaborately themed pool, but will do for lounging.
You're not walking distance to a food court or restaurant. So you may want to consider packing food and taking advantage of the full kitchen (another perk is that each villas gets its own outdoor grill).
Basically, the Treehouses seem great not only for larger groups, but people who want to spend time together as a family, as well as groups with their own transportation. But yeah, they're very pricey. Unless you're planning lots of quality time together OUTSIDE of the parks (in other words, are you a park commando, who goes from dawn to dusk and then crashes in the room to do it again the next day?), I'm not sure I could justify the expense outside of bragging rights.