I have ridden the narrow gauge rails between Alamosa and Antonito and return (& last Farmington train) and would never recommend it be rebuilt for NG.
But, I would strongly recommend that the Friends of the Cumbres & Toltec Scenic Group sponsor some kind of SG Passenger Excursion from Antonito to La Veta via the Pass and return. That would cover some very rare miles for passenger trains and include 3 tunnels and superb scenery. I would pick up and drop off passengers at Alamosa to fill the train out. That would make an interesting variation for volunteers on the C&TS and their supporters.