I agree, smaller locomotives should be financed through donations. And no, they don't all have to run at the same time. If all of the sudden there are a half-dozen little historic locomotives operating each summer, none of them will be economically self-sustaining if they are all competing with each other for the same railfan dollar. I will remind all that the success of donation-financed restorations hinges on excellent management at the top and good organization, and of course a core of good volunteers. Skilled grant writing is crucial, as no locomotive will return to operation on $25 donations. Since most grants require matching funds, good fundraising among private donors is still very important. The 315 will be finished soon, and will top out at around $400 K, and that is with mostly volunteer labor. A locomotive repair in a shop could run up to twice that, if it is on a unit that has been out of service for awile. It could still cost $600K on an engine like 463, that was retired in good working order.
The bigger steam is the responsibility of the railroads to repair and maintain. I am glad, however, that 463 has the financing to return to operation.