I'm probably in about the same situation as you, except I wish I could get 15 hours a week sailing. I'm lucking to get one good full Saturday, and usually only half to 3/4 of it even then.
First, as to why people choose to motor upwind, I think it has less to do with the difficulty in trimming the sails, and more to do with the fact that you're sailing a much longer distance to cover the same VMG, you're having to do more work, tacking the sails every time you change tacks, you're heeled over, depending on the boat and the wind, anywhere from 10° to 30°, and it's generally a longer, more laborious, less comfortable way to get where you're going. If you're out there for the thrill of sailing, then that's part of the experience. But if you've got somewhere you're trying to go, then it may be easier to fire up the motor.
Once you sail lower than a beam reach, the feedback you get from the telltales becomes useless. The sails are less like wings and more like big foils, catching as much wind as possible.
I've taken the approach -- and for God's sake take this only for what it's worth and not a bit more -- that below a beam reach the objective of sail trim is to present as large a surface area to the wind as possible. Tighten the outhaul, vang (if equipped, which mine isn't) and cunningham on the main to take out the belly of the sail, and ease the jib until it luffs, then trim it in a bit. If you go low enough, a whisker pole to put the jib/genoa out goosewinged is even better.