Thanks to Drake and Starxsword for answering my question about Eirin, i didn't know about CiLR not mentioning Eirin killing the emissaries, so maybe it was retconned out, someone should add that to the wiki.
Also Eirin mellowing out because of years of spending time with Kaguya makes me wanna ship them.
Anyways, moving on the subject of the growth of touhou's fanbase:
Around 2007-2008 I believe. It have a lot to do with IOSYS flash videos or viral ones such as the McRoll'd, which might've gotten some people curious about the series. The OST got uploaded on youtube around this time too. At any rate, 2009 was the year where western communities of otaku and japanese stuff lovers started to show some real interest in the series.
2007 seems like the year it started to become a thing, judging from gensokyo.org and walfas.org's archives.
Also apparently a english fan base has been around since
2004(!),
according to the wayback machine. Also apparently MaullarMaullar has been posting here on the forums since 2006, i think MaullarMaullar might be the oldest poster here, good job Maullar! You perverted old coot! (If anyone else here has been around for longer, let me know.)
Also, on the Japanese front of the fanbase,
HERE is the first ever touhou doujin ever made, Septentrion for a Dead Princess, released only a few months after the release of EOSD, and based on the game Septentrion. I am sharing this because i think people will be interested. Also it has a blond reimu for some reason.