Very good points.  Facing a mess is never motivating so I too do a total tidy up every so often.

I know this makes me an oddity, but I don't have a stash.  No, really, I don't.  I've got a couple cheep impulse buys sitting started (which wont ever get finished) but that's about it.  I really force myself to hold off on the next big kit purchase until I finish the one I'm on.  Doesn't help in terms of staying out of a rut, but it keeps me from buying things which I may be interested in now, but perhaps not years from now.

For me the fact that I work during the day and seasons are driving factors.  In the winter, lack of sunlight in the evenings makes me less inclined to hit the bench so weekends become key.  In the summer there is so much outdoor stuff competing for my attention each night (tending garden, mowing, house upkeep) that, again, weekends are key, and if they get chewed up with family and other chores, well there goes modeling for another week.  And so it goes a project will get neglected sometimes for weeks at a time.   Not to say I don't pick up the scalpel during the week, but it makes for my least productive time at the bench.   I really think that I could model for a living...if I could just do it during normal working hours.

I think one thing we can all identify with is what I call the "this is THE one" syndrome when you are doing something which is dear to your heart or interest and you want it to be THE Tie Fighter, THE tiger tank, THE bf-109 to end all bf-109s (or whatever) and we, literally, try too hard and end up unmotivated when it doesn't meet that standard we arbitrarily set for it.   I know for my part I have to step back sometimes and just say "this isnt the last model I'm ever going to build..." and just move on.