Well I can only express my own experiences with this "illness". I have had times with multiple kits going, a shelf of shame filling up, and more excitement building the "stash" than actually building kits. I've fought this beast for years until the wife and I built a new home.

I sold my stash of models and my cure was found. I build one before I buy one. I have found for me, I can stay motivated and focused on the build, research, planning, and gathering materials as I build knowing there is no stash beckoning me to open a new box to the smell of fresh styrene.

Trust me, this wasn't a easy process, but having very little stash actually helps me build more. I can almost guarantee all of us have had a wishlist of kits sitting on the shelf, that even given the best hopes, we will never build them all in our lifetime. Investing in a single subject has been more productive for me than investing in everything I "would like" to build.