Modern Steam

No steam locomotive ever built included all the available proven techniques to maximize its performance in service.
This fact, more than any other factor, is what lead to the downfall of world steam.

Suggestions to reduce operational and maintenance costs of museum steam locomotives

From the previous overview a few proposals can be isolated by which museum steam locomotives can be more economical. I'm only an amateur, not a specialist, so these proposals can at best be considered as well meant suggestions. It needs experts to really tell.

Basically everything is possible, if it were not for lack of funds. I arranged my suggestions by probable cost and complexity. The first proposals are simplest and less costly. I also take into account the desire of many to keep the engine at least to its external appearance in its original state as much as possible.

Porta Water Treatment
This technology can be applied without any preparatory adaptations of the steam locomotive. With a relatively small investment the life span of the boiler is greatly extended and maintenance reduced.

Electric pre-heating
This requires attaching some extra valves to the boiler, I reckon, to withdraw water from the boiler and pump it back again. This appliance will make the nuisance for neighbors a thing of the past. Volunteers do not have to rise in the middle of the night.

Lempor exhaust
To use a Lempor exhaust some reconstruction is necessary. There is a lot of measuring and tuning to do however before it works fine. It needs accurate tuning. In most cases the new stack won't be too conspicuous. The engine however gains greatly on economy and power. This investment will probably have a very good return.

Roller bearings
I'm not sure, but it seems to me that using roller bearings instead of flat bearings will give a great improvement in performance and will visible for the trained eye only. The occasional tourist will certainly not notice and if he does not bother at all.

Oil firing
Conversion to oil firing is an extensive reconstruction, but considering the Mount Washington case, quite feasible. Purists will regret it. For the greater public you can leave some fake coal on the tender, or something like that.

GPCS
If it were the choice to stick to solid fuels GPCS could be an option. I think it needs extensive refurbishment of the firebox but it will result in good and even firing of the engine and result in more complete combustion. The advantage is that you continue to use coal and maintain the authentic look and feel of the coal fired engine.