Man, powdery mildew sucks, I get it...one of my first plants came with it, so I've been battling it since the beginning...it spread to my other plant, so both plants had it the first generation, and just when I thought it was gone, it exploded, and set me back a bit...but by the end of that grow, I found green cure works really well as a foliar spray that isn't some harsh chemical. If you don't overuse the stuff, you can drench the plants, even late in flower, and the powdery mildew is gone, and the buds are fine. I had to spray about every week that first generation, but it was coming back less strong every time.
Second generation, I only ever really noticed it on a couple of plants, and even then, it was never very bad...only had to spray 2-3 times during the entire grow...so far, haven't noticed on any third generation plants....
I guess what I'm trying to say is...maybe at a certain point you're going to reach diminishing returns on your invested effort...I mean, you could incinerate your entire house, what's to stop the powdery mildew from returning someday?