While the WW&F doesn't run trains during the week, there's usually somebody there every day of the week during the summer working on something. If you're willing to chance it you could get a pretty in-depth tour, or even find yourself helping out.
Technically the Mt Washington Cog Railway is narrow gauge (by a half inch), and they run every day of the week (but only steam on the first trip). Plus New Hampshire has a number of other railroad attractions.
In Mass, Edaville might be operating, but they are a shadow of their former selves - they are now Thomas the Tank Engine Land, with less than half the track they used to have.