I've been down there - I felt it was worth the trip from Albuquerque. In that neck of the woods (probably an hour or more away) is the Very Large Array (West of Socorro), which is pretty neat, too. (You can make a geek day of it!
) It wasn't the best day of my life, but Trinity was pretty cool, and the VLA is a good thing to do with family if you're in the area.
There are two restaurants in San Antonio (W and N of Trinity Site, if you come in from the N and not from Alamogordo), the original Owl Bar (famous for the green chile cheeseburgers it's been serving since before the bomb) and another one (the name of which escapes me). The "other one" is actually pretty darn good.
If you're a green chile fan, some of the best in NM is grown in Lemitar (just N of Socorro) - my wife and I make sure we get ours from a farm there every year.