I have only done two 5K races and I've done them both solo-- and both were at Disney. I too am a mom (but I work full-time outside the home) and I LOVE these weekends. They're different than my trips with the family. I get to do what I want, when I want. As Moms, we tend to focus so much on keeping everyone else in the family happy, we don't get to relax either. My kids think it's amazing I only do one or two rides while I'm there by myself!
As far as guilt goes, my DH fully supports that my running is for our health, and therefore benefits the whole family. And that's how he presents it to the kids when they get a bit whiney. But also, we're DVC members so the kids don't get short-changed in the going to Disney department!
Disney is a great place to run solo. I have met so many nice people on the buses to and from race activities and waiting for the start of the race. I would not hesitate one bit to tell you to go for it!