I'm not really an armor guy, mostly 1/48 aircraft but I have this same problem. My local hobby shop has a bin full of used models and I can pick-up a 1/72 tank or aircraft for a few bucks. If I am involved in a particullarly detailed build or have just finished one I will put together one of these inexpensive kits. I usually tell myself that whatever point I am at in 4 or 5 hours I will quit building, no matter what stage of construction I am in. It is really refreshing to build with a new motivation, speed instead of perfection. It forces me to take shortcuts and leave out steps I normally would not; but if I don't give myself a time limit I revert to my old self and I end up saying, "I'll just scratch-build seatbelts and that will be it" or, "some brass wire and styrene strip could spruce up that plain cockpit"
THE DOWNSIDE: I am very often pleased and at the same time saddened at how well models made in this fasion turn out. I just built a 1/72 A6M Zero in three hours. All of it straight out of the box. No airbrush, one coat of paint, no masking, minimal decals. And when I was done many friends and family and I thought it was one of my nicest looking models. Making me happy they appreciate my work but sad that, what was to me, a model built more as an aide to sanity than a serious attempt at a show winner.