We usually take a walk around the museum when in town to watch trains. Eventually we just bought the year membership. I don't know if I'll go enough times in a year to break even, but I'm not worried about it, I'm happy to support the museum anyway. If you are only going once then I think the $6 is very reasonable.
One thing to note, I just received an email from the museum the other day, stating that they are changing there hours for the time being, beginning in May. The museum will only be open from 10am to 5pm Wednesday through Saturday, and closed Sunday through Tuesday.