We toured the Martin factory a couple of times (during visits related to my wife's '51 O-15), and it was very cool. The value of the tour is directly related to the marketing department "volunteer" leading the tour. We had a really good one, and one not so much. During the "not so much" tour an employee was tap-testing wood for tops, and I had to explain to the rest of the tour group what they were doing.
Of course a visit to the museum followed by some quality time in the "Pickin' Parlor" to try out some high-end and limited-edition instruments is mandatory.
If you're ever around Nazareth, PA make the time for the tour - you won't regret it.