I know of a guy who has spare bedrooms which to me would make and ideal model room. He instead chooses to work in the basement and seldom gets down there, so what's the point?
I have a spare bedroom that I use for a den/hobby shop and it has worked great for over 20 years. Right now you can't tell that I build models in there, however I can open a drawer and have my tools and a kit to work on out on the desk in 5 minutes or less, and I can clean the area up in the same amount of time as well.
I also use this den to read, pay bills, watch some TV, yak on the phone, use my computer, etc. It seems to work for me.