I've done both- gone to races solo and with family. I'm single, so if family goes most of the time it is my dad, who runs as well, and sometimes my sister if we go out east. But I'm a slow runner, so I run by myself and I kinda like that. I'm definitely a solitude runner.
Disneywise, I've done the DL 1/2 solo and w/ my dad. This year my dad and I are doing the 5K w/ my sister who is flying out and then the 1/2 by myself. I did the Princess with my sister, she stayed at the hotel and am doing the marathon next Jan w/ my dad(he's doing Goofy).
I've never had anyone along the course cheering me on, but my dad will be at the finish line cheering for me or waiting for me.
I've never had a problem running solo, b/c I've found that people along the course will cheer for me b/c my name's on my bibs.
I do it, b/c I like to keep my weight in check and to push myself as far as I can go. I'm also one of those people that if you tell me I can't do something, I will do it, no matter how hard. I also like knowing that I can do something as challenging as a 1/2 or full.
As for travel, yes! Pretty much anywhere up and down CA I will go. I also like to do one big running trip a year outside of CA. It makes the race more fun, and it gives you a chance to see the place better than just being a tourist!