For me, the fun is in building the layout, and in repairing trains.
I am reminded of the early days of a local club that embraced the Tinplate Tracker concept. We'd get together and set up the modules. After the trains were running for a little bit, most folks weren't really paying all that much attention to them. They were mostly socializing, and looking over what other folks brought (some to run, some to sell or trade).
The only trains I really like to run at all are those that I have rebuilt. I like seeing the results of my effort.