John,
Last week my wife and I did what you plan to do, travelling one day from Chama to Antonito, spending the night and returning by rail the next day. It was a pleasant evening in Antonito, even on a hot day, to walk around, looking at the Antonito yard, and to look around over near the stone depot at the third rail scars on all the standard gauge ties, walking up to the Dutch Mill to have carne adovado and a cerveza, spending the night at the Narrow Gauge Inn, eating a great breakfast at Stephan's and walking around the yards again, watching the railroad wake up, Carlos washing his loco and oiling around, then heading west across the sage on a clear mountain morning.
Its not an experience for the hyperactive I admit, but I think its a great way to enjoy the trip, and a nice way to put yourself into the frame of mind that the first travellers along this route must have felt.
Philip