...it is easy for me to wind up investing way too much time in scratch building projects, even though they can be great fun...
Important point: if it's 'great fun', how can it be 'investing...too much'? Isn't fun the point?

Heck, I never finish ANYTHING, but just making piles of pieces and envisioning possibilities gives me as much pleasure as I get elsewhere in this world. Down side, no piccies to share, of course. And, a possible embarrassing appearance on a hoarder reality show...
Plenty of modelers build, then leave it sitting on the shelf; you get to DOUBLE the fun!
And, share with us; TREBLED!
Sorry, not the advice you sought.
Doug