Somehow it must be a mixture of hard core and not hard core. If you want Chama, Antonito, the Friends and the Railroad to get behind the idea you have to be talking about a lot more that 30 or 40 extra people coming to town. If you can get all the above involved you definitely have a better chance of success, and you start off with a lot of creditability. You need to somehow make the foamers and the wanabee foamers as well as the people that just like trains HAPPY.
And therein lies the basic problem: one doesn't define the success of a photo special as drawing a large number of people. Getting the towns and the Commission excited about the photo special isn't the point.
The success of a photo special is defined by the quality of the photos participants get back, and how much fun they had getting them. Any economic benefit to others is purely incidental. As Greg, Mike, and Al make clear, get above a certain threshold (I typically use 40 participants) and suddenly the photo lines are too crowded, too many people are dissatisfied with their pictures, etc., and the event "fails."
If having a special event is important to you, it seems to me the last thing you want to do is put all your visitors onto the train all day, where they can't spend money in the towns.
Go in the other direction. Start with the basics of "Chama Days" and "SLV Days" and add some railroad events with a basis in history.
Offer a "San Juan" from Chama to Cumbres (and Antonito-Sublette). Make boarding a big deal: stage the train down at the wye, have folks waiting on the platform when "the San Juan arrives from Durango" (admittedly a little tougher in Antonito). Put Woody Woodward, L. E. Trump, and other folks who actually worked on the pre-1970 railroad on the train to tell stories and answer questions. When the train arrives, break the riders into carload-size groups with their own docent, and give them a guided tour of the site. Finish up with a picnic lunch complete with entertainment.
Rather than doing a photo special, show the folks what really happened with all those freight cars. Stage a freight at Lobato and, after it meets the regular train, have it come into town, spot empty tanks at the oil dock, put loaded tanks on an outbound train, etc.
Rather than having a "night photo session" in the traditional manner, have a guided tour of "night trains." Go through the motions of servicing several engines, and go all-out: the ambiance of a steam shed at night is other-worldly to most people, with locos gliding about, men shouting to each other, steam lit up by headlights . . .
I could probably come up with better ideas after another cup or two of coffee, but you get the idea. Build on your strengths. Photo specials are artificial creatures of necessity, not a reflection of the past. And a reflection of the past has always been the strength of the C&TS, a strength that is rarely exploited.
JAC
