this is an interesting topic. DCC seems to be *rapidly* gaining popularity, for obvious reasons. I have a 3x6' HOn3 layout, and have no need for DCC. The layout is not large enough to run more than one train at a time, or have more than one operator at a time. Still, I dream of the days where I have a layout large enough for multiple trains- and DCC would be my choice.
Non-DCC for large layouts means dividing the trackage into blocks - in other words, seperate circuits. That way, each circuit, hence any train on that block, can be controlled seperately. Selecting which throttle controls which block is done with a large switchboard - 10's to 100s of toggle or rotary switches to select whether bock "X" will be controlled by cab 1-4. Complicated wiring. When you factor in the cost of all the switches, and wiring, and time, DCC is ultimately cheaper. Seems like the cheapest decoders sell for less than $20 these days, and the cheapest controls for less than $150.
So, in my opinon, smaller layouts where operating more than 2 trains at a time is OK for the old-fashioned cab control. Any layout capeable of more than 2 trains is prime for DCC. And with the cost of DCC coming down - i predict even the 4x8 layout would benefit from the modern technology.
kevin