We do own with DVC, and at more than one resort, including the one in Hawaii. We do not own an Old Key West and Saratoga Springs (likely the ones you see on Interval) and have never stayed there, so I can’t really directly comment on those.
I wouldn’t necessarily say that the resorts are nicer than some of the other high-end Orlando timeshares, although they are all in the highest category within the Disney hotels. They’re definitely not worse! The rental rates are a matter of supply and demand, and comparing to the alternative - people who rent a DVC stay from owners don't really compare to other timeshares (e.g. Marriott, Wyndham, Sheraton), but rather to renting that same stay directly from Disney. So they can stay for $300-$400/night by renting from an owner vs. paying Disney $700+/night (+taxes) for the same room, they can save a lot of money. When you compare to other systems, $300-$400/night in Orlando for a studio is super pricy, but it's not quite apples to apples.
What makes DVC timeshares different, in my opinion is that they are more “memorable”. We stayed countless times at the Marriotts in Sheratons in Orlando before becoming DVC owners and I can’t really say that I remember the room interiors of any of them particularly well. The DVC resorts are kind of a destination in their own right. We just spent five nights at two resorts over the holidays without going to the parks (blacked out passes) and it was a lot of fun just going from hotel to hotel to look at the decorations and dining at various places.
You can’t beat things like staying in a savanna view at Animal Kingdom Lodge. Where else in there Western hemisphere do you have a Safari outside your balcony? Or watching the Magic Kingdom fireworks from your balcony at Bay Lake Tower. Or the feel of the Wilderness Lodge. Or having your own private cabin or treehouse villa with a personal charcoal grill outside the front door? And we haven’t even stayed at the super expensive places like the Copper Creek cabins or the bungalows at the Polynesian which cost an insane amount of points even when you look at it in maintenance fee cost, as opposed to rental costs.
For some resorts location cannot be understated too. Bay Lake Tower, Beach Club, and Boardwalk Villas or less than a 10 minute walk from a park entrance. Others are a short monorail or skyliner ride away. Afternoon nap? Dip in the pool? It’s a lot harder to do when staying elsewhere.
One other thing we like a lot is the room design at some places. Some resorts have studios which sleep 5, (Riviera, Grand Floridian,Boardwalk, Beach Club, Polynesian, Boulder Ridge, and hopefully more to come) which is a big advantage in our case with two older kids, a boy and a girl. The murphy beds which replaced the sleeper sofas on many places are a lot more comfortable too. And some studios have a split bathroom design with two showers (Riviera, Grand Floridian), while some 1 bedrooms have two full bathrooms (Bay Lake Tower, Kidani Village).
The dining options are also way above traditional timeshares in Orlando (of course you can go to those without staying there, and you can even park at the resort if you have a dining reservation).
There are also some perks for guests who stay at Disney hotels, like early park entry, but it’s just 30 minutes so YMMV. This year, they also added entry to a water park on your day of checkin, which we’ll have a chance to try in a couple of weeks…
