Didn't start going until 2 years later, but even by 2001, UO/IoA was a much better deal than WDW. Especially when you could grandfather your price in with a monthly renewal (I paid $12 a month for my AP until VB opened). I don't see a way a 4-park doesn't make UOR roughly comparable to Disney, which I imagine will inspire a lot more churn between the two.
Make no mistake, I think there are APs who would pay for an upgrade even if the cost was north of Disney (which it would have to be given current capacity). Let's face it, $1000+ HHN tickets sold out within minutes. But once you do that, you make a huge chunk of your APs feel like second-class citizens in a meaningful way, not just parking on the third floor and a bottled water every month. I have to believe there would be an initial backlash from that. And for a park more dependent on APs, I don't know that UOR wants to risk having to get them back at some point.