Russ:
I keep hearing about the balanced trip part of the compact, but i've never seen it in writing or heard anyone specifically reference such a paragraph. I doubt that it exists in any form that makes a real difference to an operator.
That said, I think switching to only Cumbres Turns would be bad. I would combine short trips with every double header (and in fact it's probably enough reason to do a double header in itself most days).
Take whatever normal train you run out of Chama, tack on two or three coaches for the "short trip", and doublehead the train. Unload the short trip passenters upon arrival in Cumbres. After the regular goes on East, turn the helper, reload the short trippers plus any extras who got off when they weren't supposed to, and head back down the hill.
You could of course do a separate short trip on days when the train leaves from Antonito as an independent trip.
I'm not sure how you'd make money on this, but I suppose you could -- the loop charges $16 for an 1.5 hour round trip; maybe $25 for a Cumbres turn of 2.5 hours would make the dollars work out? You'd leave around 10, get back around 12:30. It'd extend the lunch rush for Chama restaraunts by a bit, which would help the locals, but how many people would you need to cover the wear-n-tear and labor?
Since folks in a hurry are most likely day-trippers, the normal Saturday double header should be often enough for the short trip to start, and super simple to do as well.
Tom