I just started using the default settings of Kupo's Brawl_.txt last night.
To be exact, so there's no confusion, these are my current settings, using the exact names from the Brawl_.txt file (I have no idea what the actual numerical value modifications are):
No tripping
no replay time limit
Auto l-canceling
hit stun
Lagless ledges
No ASL
No decay
up/down gravity
Stage reversed
Buffer
dash dancing
CD Hack
Triple Jump fix
Hitlag division
Shield gain
shield stun
Disclaimer: This is merely my opinion, and regardless of what I think of balance issues, I think you've done a great job at doing all this testing and modifying thus far.
At first, I was just messing around in training mode, but I started playing around against CPUs (haven't gotten to play live players yet), and something really stuck out to me. Having the No Decay on is just too ridiculous, imho. Also, the way the current hitstun is set seems FAR too long to be left completely incapable of avoiding attacks. Something has to be changed, because right now it's feeling a bit too much like SSB64 (where almost no one lives past 60-90%), except the moves in Brawl do way too much damage since there is no decay, and are too easy to combo, imho.
At first, I was okay with the ALC thing, but even that seems a bit much now that I've seen what some characters are capable of. Shield grabbing is impossible against most aerial attacks and I think it gives too much of an advantage towards offensive pressuring to those who have good SH heights. I think this could be solved by reducing the difference in frames (I believe it's at 50%, so maybe it should go closer to 60-70% of the actual number of frames to land).
Another thing that is a bit crazy to me is how much the characters slide. Is there some way to increase traction, because my Link is literally sliding all over the place even when I'm not using DACUS. I believe it was something that was just native to Brawl, due to the increased floatiness, and thus it might not be something that could be fixed without screwing over mobility. I still think it would be nice if the traction could be upped just a bit, though.
EDIT: On further evaluation, it seems as though the shield grabbing is only a problem with Zelda, Link, and ZSS, who all naturally have slow grabs. Shield grabbing is fine for the other characters with "normal" grab speeds.