Once you have done the Marathon, are the other races simply shorter versions of the same thing? For those that have completed one, have you found it rewarding enough to make up for the aforementioned negatives?
I did my first marathon as part of Dopey. Before registering for my first Dopey, I had completed 9 half marathons all at
Disneyland or Disney World and the Star Wars race weekend challenges (10K and Half on back to back days) in 4 consecutive years. Aside from the marathon aspect of things, I already had a solid foundation on races at Disney including the theme park side of it after the races.
I reasoned that if I could complete the marathon I could also complete Dopey and since the marathon could have been a one and done for me, I opted to go for everything. Again I concluded that if I finished the marathon alone and hated it, I would kick myself for not having run Dopey and then have to do a second marathon just to finish Dopey. Honestly, I'm not sure about the rationality of that approach, but it was my reasoning. It turned out that in a weird way I enjoyed the marathon and have since run 2 more Dopey Challenges.
I discovered in running races that I usually spend the first two miles or so of any given race wondering what I had gotten myself into. When I ran my first challenge race, I learned that I worked through all those negative thoughts in the first race, which allowed me to be in a good place mentally heading into the longer race(s). This pattern held true with Dopey. On the day of the half and especially the full, I'm confident in my training and focused on the task at hand. Pre race jitters are pretty minimal which helps me run my best race which at Disney includes a lot of time enjoying characters and such.
Now as others have said, Dopey absolutely alters your park time. Except for 2021, I have been to Disney World every year since 2017 and spent at least one week there each time. So I can feel okay about reduced park time because of Dopey. Until this year I went to bed very early before each Dopey race. This meant leaving the parks no later than 6:30 or 7:00pm the evening before a race. This year, I enjoyed Rise of the Resistance 3 times the night before the 5K and went to bed at 11:00pm. That absolutely had an effect on the rest of my race weekend because I was in a large rest deficit even before the challenges that the half and full pose. Now, I still had a great time and have no regrets. But the sleep deficit from not going to bed early even one night before a Dopey race impacted the rest of my trip.
This year is the first year that I began to understand why more experienced Dopey runners sometimes say that the hardest part of Dopey may actually be the 4 consecutive early mornings. When you've run the marathon, you already know what that takes. In my specific case, I'm already running 5 days a week so the 4 consecutive days of running really isn't that big a deal for me.
For me perhaps the most enjoyable part of Dopey is the varied course experiences. The 5K goes around World Showcase which is probably my favorite part of Epcot. Seeing the torches lit before sunrise and sometimes being in World Showcase during sunrise is a great experience. Likewise running the 5K helps me truly savor the moment because when I see World Showcase during the full, I'm very much ready to cross that finish line.
As a back of pack runner, I do not get to see Cinderella Castle when it's still dark out, but I do get to see it at sunrise or shortly thereafter. This year was especially pretty with the first light of the morning reflecting off the colors of the castle for the 50th anniversary.
Opinions on what constitutes worth it will vary. So as much as seeking the varied experiences here is a good start, you also need to evaluate your reasons for Dopey and just how much you can live with impacted park times. I got to Epcot around 4:00pm the day of the marathon for a 4:45 dinner which was also my first real meal of the day. I hopped to the Magic Kingdom for the fireworks and to see Mickey. That's a different kind of park day. As a frequent visitor to Disney World, I can live with that once in while, but a rare visitor may feel very differently.