Before people consider this there are a few basic things to look at. Yes, the IRM did have around 40,000 people there for their Thomas weekend. But also remember that within a 2 hour drive of IRM is a population of over 6,000,000 people. 40,000 folks equals less than 1% of the population now translate those numbers to New Mexico and examine the cost factor. Plus in the Chicago area you can't walk into a mall or toy store without Thomas merchandise slapping you in the face so the exposure is constant.
Right now the best thing to do is go after the tourist dollar based on the simplicity and beauty of the region and hype the hell out of Chama Steam to get as many railfan dollars as possible. Use some of these proceeds to create a promotional fund solely for the purpose of promoting the area and its events.