This is what was so surprising to me, since I thought the same as you. But yep - the +50% coin promotion, like other coin stuff applies equally to coin purchases and credit card transactions.
This was a… powerful thing to realize after already spending a whole lot of money that I thought was going to go significantly less far!
Heck, when I made the initial purchase I didn’t even know one coin = one yen, I assumed it was less since I ended up with so many, so it was a nice surprise all around.
I spent a lot of time the last couple weeks ogling books and making a checklist. The coin largesse somehow didn’t make a dent in the number of items on the checklist… but it did significantly lower the average level of “gotta get it”-ness to a safe “that would be pretty cool to have sometime”!
Watch out though! 2021/3/24 09:59 in Tokyo is… 4 and a half hours from now (did I get that right?). And the coins take a little while to trigger so the cascade will be significantly less powerful soon.