I have 01 Forester and 02 WRX(bought new). Have cleaned the engines at least once a year and never have had any problems.
I spray everything down with diluted APC, then scrub and wipe, then rinse. If you have access to compressed air, blow all junk out from under the intake manifold(yours is probably covered with plastic) first before you get it wet.
One thing I cover is the altinator(some say you don't even have to do it) with plastic grocery bag on both, and the exposed aftermarket intake on the WRX. Never had any issues. I do not presure washer, but do use strong stream of water to rinse. I have applied more dielectric grease to every electrical conection that I can find though, but they are already packed with it from the factory.
Did clean my old Isuzu Amigo engine with the coin op car wash pressure sprayer not long after I got it. Had to sit there for a couple of hours before it would fire up again. Not fun, but no real problems. Had it for probably anther 10 year after that.