+1 on purchasing the legacy as well! not that i hate the merc, and that i have only so much knowledge of it, but that because running a legacy in japan will always be cheaper and the access to well regarded mechanics and parts are everywhere - think Trial, Subaru and STi itself, and other less known to the outside world local companies that do a good job in subaru maintenance.
and yeah, think about swapping out the twin turbo (when it dies), as i saw on a forum, the wiring harness for the stock twin turbo is ridiculous. 30+ electrical wires in a box, head explodes for me. if you ever send the car to australia, do you mind doing a write up? since i would like to know about it just for knowledge purposes...
also, for legacys/liberties in australia, i think the market did not get the turbo version wagon (?) till the 4th Gen, which is the BP/BL chassis code versions. any older liberty would most likely be a GT hood swapped onto a non turbo RK/RX Liberty, whatever the top range offered was.
and the merc, well maybe another time anyway, would probably make it stock VIP style if I had one, dunno for you.