What sort of leakage reduction could I expect if I try to plug all these tiny gaps?
This is a typical cathedral ceiling around these parts, 2x6 tongue and groove over 4x beams. In this image we're looking at a big valley rafter running diagonally in front, with a beam in the background at right. There are a couple of can lights and a couple of skylights in there too. This is after about 30 minutes with the door running and a 20 degree delta T. All of the beams have strips of trim, about 3/8" x 1", nailed on with brads. Lots of air comes out from behind that trim, where boards end. Relatively little comes out in the field, apparently because there's poly sheeting behind the 2x6.
It would be possible to pull each piece of trim with a flat bar, pull the nails, caulk behind it, drill a hole into each joint, inject more caulk in hopes of sealing the tongue/groove, and renail the trim. Some of this stuff is 16 feet in the air above the grand piano, really hard to get at.
Ever done a test-in, test-out on leakage like this? Did you get big results? This house is well around 2 CFM50 per square foot, so it needs a major reduction.
I have sealed this before. IMO, it would be easier to run two beads of caulk on each side of trim rather than removing the trim piece. Unfortunately I didn't individually test the measure when I did the job, so I am not sure how much that contributed.
I've worked above expensive furnishings and either everything has to be moved or protected. Drop that flat bar and no one is going to be happy. Thus, I might consider the back door approach. Do everything else and what is left is some base amount plus that ceiling. If you can isolate that room in any way, some zone pressure readings might help identify how much is coming from where. Again, even if you can't read that space, maybe you can read others. Divide and conquer.