The motor won't blow under 1800. It'll run rich. And the problem is really only at WOT under 1800. Is that really risking blowing the motor?
And as for risking poor idle for power, I guess you'd have to ask anyone who's ever put upgraded cams in anything...
So far, the only real evidence (including anecdotal) I've seen about the effects of an aftermarket intake on an NA, maf-based Subaru is the thread on nasioc by williaty (
http://forums.nasioc.com/forums/show....php?t=1471819)