Personally, the on-course entertainment is more a distraction for me than a requirement. I almost prefer the races at
Disneyland because, overall, I like the weekends better, I like the courses better and they're just easier for a participant.
Also, the deferral thing doesn't bother me either. Major races (NYC, Chicago, etc.) don't offer anything in the way of deferrals. Can't make it? You're out the race fee. Maybe you get a guaranteed spot the next year, but you still have to pay for it again. I lost over $200 for the NYC Half this year when I got hurt. I have a guaranteed spot for next year - if I fundraise again, which I won't. So, lesson learned.
I think that RD painted themselves into a corner with TA's for WDW races by now requiring a ticket purchase and minimum two-night stay at a hotel to purchase a bib through a TA.
One of the BIGGEST RunDisney TAs (Get Sports) decided that they would no longer sell races at WDW in 2016 because it just didn't make business sense to them to do so. Another major TA that I've purchased through before opted to not take an allotment of Princess bibs because they've had to fire-sale every race.
Plus, I think pricing has driven them into a pretty hard market correction. Registration has reverted to previous form, but it's for different reasons. I'm glad the 5Ks now have metal medals, but I'm not paying the asking price now for what is offered (small medal, unisex shirt). On top of that, the market is over-saturated with races. I don't think there needs to be two Star Wars weekends. I like Tink Weekend, but I don't think you need two women-centric race weekends either. And I think the dumbest move they made was taking their one unique race and tossing it aside for the ultimate money-grab: the two-race challenge.
A lot of participants these days are one-and-done as well. Check it off the bucket list and move on to the next fun RunCation (Rock n Roll Race, SeaWheeze, Napa-To-Sonoma, Surf City, Bos/Chicago/NYC, etc.).
I'm not worried about races selling out. If I start seeing a drop off in the amenities that I feel my money is paying for (like medals start becoming smaller and poor in construction), or race shirts are a drop-off in quality, or on-course support takes a significant drop in quality. That's when I will stop altogether. I'm already scaling back significantly in 2017.