For me the question is what is most satisfying. It used to be simply looking at my trains on shelves. We graduate to different phases of our hobby. I imagine, I must have thought that if looking at trains on shelves made me happy, a layout would make me happier. I was amazed at how wrong it was for me.
It's the process. The building, the people, the stories, the photography and, simply, creating something from nothing. Of course, I love to watch trains running, but I love lots of things. Music, stamp collecting, sports, photography.
Collecting trains was, and is, fun. Putting the collecting into perspective and balancing all of these other pursuits is more fun. I now have the freedom, albeit a psychological freedom, not to go to all of my usual haunts looking for a Eb6-Q2 Carmel Southern Pacific, LOLOL. Besides all of the dollars not being spent on trains, I am amazed at all of the hours I now use for other fun. Learning new guitar techniques, for example.
Trains are in my blood. They always will be. I do love, however, being less one dimensional. There is an incredibly talented layout builder, Malcolm Furlow. He built the San Juan Central. Then he decided to be an artist.