Apparently the new microSD I bought was UTTERLY BORKED. h2testw results gave me a 400MB GOOD 30GB-DATALOST summary. Had an angry chuckle at that, so much for buying unbranded Chinese crap online (and it actually shipped from CHINA too).
So I bought a new one, a Sandisk branded Class10 32gb.
AND NOW IT'S WORKING AGAIN!
But I had to say goodbye to my Activity Log, my games and saves, my Mii Plaza -- EVERYTHING, from circa 2011. Now I'm trying to gooooogle if I can just download shit and UNLOCK EVERYTHING for my Mii Plaza. Also trying to read about Pretendo and that other thing about trying to Streetpass online. (GOD I still remember setting up HOMEPASS and getting tags from all over the world, good times)
EDIT: Also I tried Universal Updater - NO GO. Apparently my ISP got it blocked or something, because it refuses to load on my browser, but going to a website checker it registers as up. Same goes for the QR code and file links for 3hs (hshop), so.... I might have to go the circuitous route to go get some of my favorite games back. Things like Culdcept Revolt and Etrian Odyssey IV and Elminage)
Oh and redownloading games from eShop is an absolute bitch, goddamn, I forgot how much I hated downloading games from there