I've done all of my RunDisney races as solo trips, with the exception of maybe one with my daughter (but ran it solo since she is fast!) Honestly, I love it that way. I can do my own thing--which doesn't mean being totally alone unless you want it to. I have met many people through the earlier disboards RunDisney forum that I still see on race weekend--meetup, dinner, parks (if I wanted, but I usually do that on my own). And with this version of the forum, there are even more people to meet if I want.
Not Princess weekend, but in 2018 I ran Dopey. Some random guy pegged my pace during the 5k and asked if he could run with me. He was also doing Dopey and so we ended up running the 10k and half together. He was injured for the full, so I ran that on my own. Never would have planned on it, but it was great that it happened.
So "solo" can be be "really on my own" or "stuff with other people". There are lots of flavors of solo.