I ask this question because I seem to be one of relatively few operators who, usually, keep my trains as they were when they were out of the factory.
This means no electronic upgrades, no motor swap outs, and no changes that can not be reverted back to original conditions.
For example, all of my (both conventional and TMCC equipped) Lionel LTI and older LLC period locomotives are still running with older, out dated sound systems and, depending on which engine, AC Pullmor motors. I do modify some of my Postwar engines, but nothing that can't be reverted back later on. The only time I did some big change was upgrading an MTH PS-1 engine to the 2.0 system.