Hmm, interesting dialog going on here. To me, 3 rail scale would be exactly as already stated...getting as much scale detail as possible within the scope of using 3 rail track/trains. What is so tough about that?
For me, trains started under the Christmas tree like I am sure they did for most everybody here. Lionel, Tyco and an Aurora postage stamp set. I believe in that order for me and then it just kept on going. Now 52, I have built in N scale, HO scale and G scale in the garden. I've messed around with a little live steam and done a very small O scale 3 rail layout.
I am now planning to build an O scale layout in my office/man cave. For me, I love scale, as close as I can get, but I also have financial and space limitations like most of us probably do. Oddly enough, I have my heart set on the MTH line of AEM-7's. They don't come with the ability to easily go from 3 rail to 2 rail like a lot of the company's other offerings do. With the factors at play in making everything work in 2 rail, I have decided to just stick with 3 rail. So for me, it comes down to compromise and practicality. Yes, part of me wants to go 2 rail scale, but reality tells me that for what I want to accomplish it will be a more practical road to go 3 rail scale....
Look forward to sharing with everybody.