Dave,
If you look at the photos of the recent Trains Magazine charter that John West posted, you will see two busses at the State Line crossing. These were transporting the charter participants from Chama to Cumbres and stopping for a number of line side shots that would have been difficult to achieve from the train. Other charters have done the same thing.
Of course, you can do what some do and that is buy a ticket and chase. Two people can even share a ticket and one ride while the other chases. Several people have done this on recent Friends charters. One rides Antonito to Sublette or Osier and then they trade off.
That said, getting revenue from chasers has always been problematic. Some feel entitled to free shots, others are merely thoughtless while a few can sometimes be prompted into making a donation to the Friends of the C&TS. My feeling is, appeal to folks better nature and suggest that they consider joining the Friends or at least making a cash donation. Without the Friends, there would be no historic freight car fleet and very few charters for anyone to ride on or chase.
A purely chaser event is unlikely to succeed, but a van or bus from Chama to Cumbres, followed by exclusive back country locations is a model that works and can sell. That said, chaser events have succeeded on other railroads, but generally because they were organized by groups with tightly controlled mailing lists, flying under the radar and therefore attracting few non paying chasers. The C&TS, with the web cams and active internet exposure would have a very hard time managing such an event.
Michael Allen