Yes, Traffic does pick up in at harvest time. I lived in the San Luis Valley for many years in Del Norte.
There used to be a sawmill in South Fork and the SP/DRGW at the time sent three trains a week to South Fork to get a few loads of sawdust form the mill and occasionally a lumber load or two. That quit when the sawmill closed. Since then the only activity on the line west of Monte Vista has been car storage and a few trips to deliver equipment to the Rio Grande Historical Foundation in South Fork. There is traffic from the Coors facility in Monte Vista, and some agricultural industries there. There is traffic from the Rio Grande Central, and some traffic from the Perlite facility and a couple others just south of Antonito.
There are also a few grain elevators between Alamosa and Monte Vista that produce a few loads each year. I don't know what the status of the concert site at fir is, but I believe it was destroyed in the Spring Creek fire last year. I don't know if they are still running tourist service between Alamosa and La Vita an more either. I road that train a couple of times when I lived in the area.