Last month, the RENFE office near the Pilgrim Office on Rue de Villar in Santiago did not sell/issue the Tarjeta Dorada. They said to get it at the train station.
At the train station, the ticket agent gave us a 40% discount on the TrenHotel to Madrid based on our ages as shown on our passports, but did not require us to purchase, or pay for, Tarjetas Dorada.
The TrenHotel was great, although having dinner at 10:30 seemed pretty late to us, fresh off the Camino. After sleeping in Alberques for a month, the noise of the train didn't bother us at all and we slept well.
It's the slowest train in the world - it needs to be to stretch out the ride so it can be an overnighter. The other trains coming in had these sleek, space age, locomotives. The HotelTren is pulled by something that looks like it was built in 1960 or so.
We loved it and would do it again.
Karl
From the station, it was an easy, fast, and cheap subway ride to Puerta del Sol, where our hotel was.