I was exercising my credit card... AGAIN. Sometimes I wish I had the foresight to buy the Collector's Editions back in the day.
Thanks to my trusty US human mailbox, who opened my items and sent me the codes (because I was paranoid they'd be lost on the way over) I could upgrade my account quick smart (and maybe it was also that shipping within US is free - sending it to me was $50 each). Arvash told me you can just enter the code on top of your old account and it gets upgraded. I wasn't sure what would happen if you tried to put the Collector's Edition code on top of the existing BC/WOTLK.
So, that makes a lovely round number. Which probably won't last for long, because I have another one coming... but I'll at least remember this moment briefly.