"When does it end?"
As Lucas said: It IS a very slippery slope.
Refine, modify, scale wheels, fixed pilots, Kadee couplers... all of that... and you still have the center 3rd rail to accept mentally.
I started down that slope several years ago: When my 3 rail stuff started edging closer and closer to "scale"... I reached a point that I was no longer able to accept the 3rd rail. Frustrated, I switched to scale S (not S Hi Rail) and love its size and proportions... but not too crazy about having to "seriously" model in order to complete most projects. (i.e. Assemble kits, or modify models, adding details, installing DCC/Sound components, painting/decaling/weathering, etc.) I find my modeling "energy" doesn't sustain month after month for me for such modeling. I have to take looong breaks.
I've added 3 rail back to my reportoire of trains... BUT... I'm staying well within my 3 rail "comfort zone" and "playing trains" as opposed to making the attempt to make them as realistic as possible. Hopefully this approach works for me.
Agreed, this gives me 3 basic mediums that I indulge in when the mood strikes:
* V scale for my 1880's - 1900's kick.
* S scale for my scale itch.
* Traditional 3 rail for "playing".
BUT... I hope it works for me. We'll see.
Careful on how much you inch toward that slippery slope, your findings may be the same as mine!