In terms of layout design and certain key accessories and structures, I agree with rrman (the OP), and am unlikely to make changes. My wife and I have no plans for relocating, and enjoy our current modest-sized home, which has a half basement. This limits available space for a layout, my current layout is about 25 years old, and I have already maximized it size.
However, I've recently decided to make other future improvements/changes to hold my interest.
First, I have a town on the far left side of the layout in which I plan to rotate the structures and periodically change the scenery. I recently decided to do this because I started to collect Plasticville. Since I have more Plasticville and other structures than can fit on the layout, I plan to rotate them every 2 to 4 months, with corresponding scenery changes in that section of the layout. When I make such changes, I plan to take numerous photos and videos showing trains running through the town, and posting them on the Forum.
Another future change is to have the layout evolve over time to add features so it is more like The Put.
If I become more ambitious. I could tackle the wiring, which is a major project. What I currently have is functional but unorthodox (my own creation) and not well organized, so I could rip it all out, re-do the wiring by the book using bus wires so there are much fewer wires, and also color code all the wires. I have model railroad booklets and train magazine articles on this subject, so I know how to re-do the wiring.
Another major project could be improving the roadbed and ballast for the track and replacing some sections of track. However, I have always liked Lionel tubular track and 022 switches, so I have no plans for changing that.
During the past 6 weeks, I added the DCS remote set to my layout. So far, I am very pleased with it. Arnold