If you're ever in San Diego, this is definitely worth the stop. There is a historic park to check out, lots of great Mexican food, and fun little shops and museums. Old Town is also home to the Mormon Battalion, which was such a lovely tour (I cried twice).
I met a very nice lady, Syndee, while I was walking around. She offered to take a picture of me and so I did the same for her...then we found out we were both from Utah. We spent the rest of the afternoon touring around together and it was so nice to have the company! I know of people who prefer traveling alone because they meet so many interesting people that way. I'm finding that to be true on this little venture. It has been one pleasant surprise after another.