I have taken the route from Denver to Raton (and back) to catch the SWC a few times.
It has been a couple of years since I did the DEN to RAT but did the RAT to DEN in March.
From what I can remember from past trips, it seems the passengers on the thruway bus have mostly been Amtrak passengers. I think there have been a couple of people who get on and off in Colo Springs and Pueblo once in a while.
The bus ride is nice because there have been so few passengers on it. It has never made sense why they would run the big Greyhound bus for so few people(usually 5-10). The bus is old, have never had it break down on this route.
There was one time the bus did not come to the Amtrak station, this was some time ago. The Amtrak employee came out, said the bus was late, he was calling a cab. The cab took us to the Greyhound bus building. The bus was about two hours late. When we boarded that bus other non Amtrak passengers boarded but there were maybe 10 people on the bus. I think there were only 2 of us for Amtrak and one non Amtrak who went to Albuquerque with us.
We missed the train in Raton and the bus driver stopped at McDonald's for us to get food because he was taking us to Albuquerque. When we got back on the bus in Raton, the driver said the bus was now a charter. We just barely made it in time for the train in Albuquerque.
One time one of the thruway bus drivers told me, they drive DEN to RAT, stay in a hotel all day and then take the Amtrak passengers back to DEN.
But...on my March trip, RAT to DEN, the train was maybe a couple of hours late. There was not a bus waiting for us, which there usually is, with no Greyhound passengers. The wind was blowing hard, it was snowing, we are trying to ask the train what to do. They said a bus was on it's way to wait inside. I asked what if it doesn't come? I was told to call Greyhound. I was nervous being left in Raton like that, there is nothing in that station but some seats and restrooms. There were about 5 of us waiting. A Greyhound bus did come and it was almost full of Greyhound passengers, it was kind of awful trying to find a seat. And it was an old old bus but we made it to Denver. This has me wondering, do the drivers spend the day in Raton waiting to take people back or did they change it? What happened to the bus that should have been there for us? I will never know.
One of things that worries me on this route in the winter is snow over Raton Pass. Once in a while they do close it because of snow. That is the reason I only did the one way in March(RAT-DEN) I saw a big storm moving down there and was nervous about missing the train and did not want to spend a day of my vacation stranded in Trinidad or Raton. So I opted to take the Greyhound bus to Las Vegas(I think it was on here I learned they have new and refurbished buses going out of Denver). It was a very pleasant ride. The bus was shiny, they have wifi, it smelled good. However, the seats are really small and no leg room. Turns out the roads did not get bad down there but I was able to see the better Greyhound buses.
I have always enjoyed the bus ride down to Raton, it is always an old bus but the bus is not full, it stays clean, restroom stays clean.
One thing, take some drinks and snacks for the thruway ride, then you have them if the train should be late in Raton. There is some kind of store across the street from the Raton station which I think has snacks for sale. There are vending machines in Colo Springs, not sure about Pueblo(new station I haven't gone in). The bus used to stop in Trinidad at a gas station with snacks. Not sure if they still do or not.
Also from the past, the Denver station opens at 5:30AM, the bus leaves at 5:30AM. At the temporary station I had been able to quickly go in and use the restroom in the station once they opened before the bus left. I don't know if this is possible at the new station, restrooms are downstairs, not sure where they will be when they fully open the station.
The restroom on the bus has always been clean for that trip.
I hope this helps!