It is a balancing act. At some point, your hobby, be it trains, cars, guns, etc, can take over your life. One can get to the point of spending every free minute working on their hobby of choice. You have to ask yourself "Do I own the _________, or does it own me?" I am guilty of getting tunnel vision when working on my projects. If I am really into a project, or want to get to a certain point before I take a break, I can spend every free minute working on it for day or even weeks. I try to make sure that I make time for my wife and kids and all of the other necessities around the house. We have to remember that these are only hobbies, not necessities.
If you can walk away from your layout for a week or two, then it is not too big. If you have to continually perform maintenance, repairs, construction or what ever else, the layout owns you and it is too big.
Tom