As someone who is the son of a CM, I find myself very lucky to have been able to have gone to WDW many, many times over. If I had to guess, I'd say I've been to WDW at least 100-125 times since 1982.
I'm now almost 40 and I STILL love going. In fact, for the sake of access, I ended up purchasing my first AP ever this year despite all of the times I've been over the course of the past several decades.
Some of my thoughts about my repeat visits:
First, let me say that my fascination with WDW is pretty much solely with the parks themselves. I'm not big on the Disney brand per se as far as the characters, movies and such, but I absolutely LOVE going to the parks. Call it fantasy, call it escapism, call it whatever you want, but going to the theme parks and soaking up the atmosphere and enjoying the attractions/rides (especially the dark rides), and all of the little details that come with the parks, is something that is nothing short of magical. It really is like being able to forget reality and be in another world--at least for a few minutes at a time. This is also why I find myself listening to a lot of audio of ridethroughs whenever I want to feel like I'm back in the parks and on the attractions.
To someone who would ask what someone might get out of going to one of the parks over and over I'd ask if they ever watch a movie more than once. Most people do buy movies they like so they can watch them multiple times because they like the mindset or atmosphere the movie puts them in. However, for me, being on a ride or an attraction at Disney is FAR FAR more immersive, mesmerizing and atmospheric than a film on a screen, and is something I enjoy experiencing each time. And with the amount of detail that is associated with the architecture of the parks as well as the attractions, there is always something new to see or that I didn't notice before.
Now, I will say that I can only justify my many return visits because up until this year when I bought a pass they have been free because of my dad working as a CM. If I had had to pay regular park tickets there is no way I would have gone to WDW nearly as many times as I have over the years, but I definitely would come back when I could afford to because the experience I have at the parks is so wonderful.
I will say that over the years the crowds seem larger, the wait times seem longer, the CMs seem overwhelmed and in general the top-notch quality and high standards of maintenance and upkeep has gone down while prices have gone up. But even with all of this into consideration, I think the cost for what you get when it comes to the parks is still a great deal. I can certainly see value diminishing if I had to pay for a park ticket each time, but I think I'd really have to go a lot for it to ever lose the special feeling it gives me every time I enter one of the parks.
I'd also say that I certainly see where it would be very difficult to return if I had to pay for park passes for a family along with hotel stays and the food and such for a family vacation. When you start talking about that kind of money I can certainly see a diminishing value, especially during a busy season when crowds are bad, lines are long and it's nearly impossible to get in anywhere to eat without a dining reservation. I always know there are those out there who can't afford to come often or come at times when it's too crazy for the parks to be properly experienced and so I never take being able to go so often for granted, especially when it seems like I hit a perfect day with low attendance, beautiful weather and can truly appreciate the wonderful parks of WDW.