You're definitely right about insulation upgrades being a game-changer for energy bills. I've seen folks shocked at how much money they were literally letting slip through their walls. Spray foam especially seems to make a huge difference, though I've had good luck with blown-in cellulose too—depends on the house, I guess.
Funny you mention moisture issues...I swear, every time I open up a wall near a window, it's like playing "what surprise is waiting for me today?" Mold, rot, random critters—I've seen it all. Had one job last summer where we pulled off siding panels and found a whole colony of carpenter ants having a party behind the insulation. They weren't thrilled about being evicted, let me tell you.
And wasps...man, they're sneaky little jerks. Had a similar experience to yours once, but instead of shutters, they'd built their nest right behind the fascia board. Didn't realize it until I was up on the ladder pulling things apart and suddenly had a swarm buzzing around my head. Let's just say I set a personal record for ladder descent speed that day.
But seriously, sounds like you're handling things pretty well. DIY projects always have their curveballs, but that's half the fun, right? At least that's what I keep telling myself when I'm knee-deep in drywall dust and regretting my life choices...