Reaction to Methods seems highly polarized: almost every review of it I've seen either falls over itself to gush or sees it as pretentious and self-indulgent. Age and gender seem to matter less, by that stage, than contrarian tendencies and tolerance for what tvtropes calls an author tract, but the demographics of fanfiction readers are weighted heavily towards people in their teens and twenties already, so samples of older readers are small. The particular characteristics of Methods do probably push it towards the older end of the scale.

Since that's more or less the demographic that LW attracts already, I'd say that Methods, and the rational fic meme more generally, are effective as advertising but ineffective in broadening the site's appeal.