I stay motivated by 'multitasking' while I model/paint It feels more like a social activity than a lonesome project when you sit on the couch with room mates, friends, family, who ever! while you idly
de-spew and clean models or base coat a full set of models, do the highlights, detail, etc.
In my opinion doing a set of models production line style is better than doing them individually it feels as though you're getting a heck of a lot more done when you set down those 10 terminators all base coated and ready to highlight rather than finishing one off completely down to the finest detail then going "Holy crap I have to do that 9 more times."
This is especially true when you're cutting and cleaning a large number of models! It's a tedious process
de-sprueing troop after troop after troop. But when you have something fun going on in the background time flies right by. I've cleaned around 50 marines down to the grenade this week and still going strong.