I don't like the idea of defining fun by whether or not you are fast enough to take a photo with a character. Don't define your experience by the photos you didn't get.
1. There are a lot of really neat things to see besides characters. During the 2011
Disneyland 1/2, they had the parade floats and the Disneyland Railroad trains out along the course where you could see them in great detail as you walked past or even get a brief photo if you had a camera with you. These would have had very short lines at worst and gave you the opportunity to have a neat photo you can't get during the day.
2. Enjoy the opportunity to see the parks in the early morning hours and/or when they are extremely empty compared to what you're used to. During the 2012 Wine & Dine 1/2, I got to see Animal Kingdom at night. The World of Color fountains are beautiful in the first rays of the morning.
3. For me the fun of characters is not in getting the photos, it's in interacting with them. Chip and Dale once did jumping jacks with me to help me prepare for a race the next day. They also did paper, rock, scissors after a race to determine which one of them won that morning. On another occasion, the chipmunks decided they would bite my medal to make sure it was real.
During the 2016 Star Wars 10K-The Light Side, BB-8 was on the course. I'm a very slow runner so his line was cut off and I couldn't even get in it. The next morning during the 1/2, the line was estimated at 20-25 minutes long. I could have chanced it, but didn't want to risk it. I "settled" for a couple of selfie shots as I went by. Well, I was in Disneyland again this past July and saw where they had BB-8 next to Rey's speeder from The Force Awakens inside Launch Bay. Suffice it to say, that picture next to a nice prop replica from the movie is much better than the one I missed out on because I was too slow in January to take a risk.
I also heard of some runners that were swept from the 2015 Star Wars 1/2 and couldn't figure out why they were swept since they were averaging 9.5 minutes per mile when they were running. Except they were not running during the multiple 30+ minute character photo ops inside the parks.
Don't get me wrong. Character photo ops during a race are fun if you can afford to stop. But Chewbacca celebrating my Star Wars medals and Darth Vader seeing the medals and accusing me of being sympathetic to the Rebellion were much better moments than had I stopped to see them along the course. I think character medal photos are a lot more fun than character race photos. If they're rare characters, take your best selfie and keep going. Don't let a photo or lack thereof define your race. Let your success in persevering to the very end and finishing be your defining moment of greatness.