I am sure a lot of the dozer use on the NG was due to convenience as well as cost. When I did the Rotary in 1993, I had a nice chat with then GM Joe Vigil at Cumbres as the train prepared to do battle on day 2 of the proceedings. He told me it cost the RR about $10,000 per day. I think 93 was 4 days, so figure $40K. So today I would imagine it would be $60-80K since we were 25 years down the road in 2018.
Even when the rotary ran, they used a dozer sometimes to clear some places, like the one leg of the Cumbres wye!
In 1968 we chased the first empty train from Farmington back over Cumbres toward Alamosa. The railroaders told us the road engine with the train(483) would be stopping in Osier to pick-up a dozer, and do some other switching along the way. Therefore we went to Antonito and chased the helper back to Alamosa(493), and never saw the freight as it arrived well after dark. We did shoot pics at Tanglefoot and Los Pinos though.
Greg
PS I believe Russ shot the last run to Alamosa and they picked up a dozer near Toltec I believe. I think they had some work to do back there during 1968.