just done some more reading - yes you can do - apparently Samco do a replacement hose which does away with the 'pre-turbo resonant chamber', this chamber is responsible for quite a bit of air swirl as the inlet and outlet are not aligned or matched
Just checked your engine bay shots - I see what you mean now, although I havent done it myself there are plenty of examples of people just replacing the big plastic box with a piece of pipe - Subaru themselves did away with it a year or two later than your model
wrt the powder coating wheels - I have done car and bike wheels with no problems, I certainly wouldn't have risked a wheel failure on my bike - If I was running wheels purely for the track I would paint them to save weight but I have always have the work done at specialist wheel refurb and powdercoat places.
Does it seem a bit more of a coincidence that it appeared to be the same type of scooby wheel that failed??
No they are different - the head gasket goes between the head and the engine block, normally metal, the rocker cover gasket is normally a piece of rubber that goes between the head and the rocker cover
stick with 5w30 and millers is a good brand - if you are in any doubt contact Tim - (Oilman) for his recommendation or check the Opie oils recommendation site on ebay
http://stores.ebay.co.uk/opieoils/pages/engine-oil-and-filter-service-kits
I would do the reverse of what Farmerpug did just get standard shocks with STI springs - cant remember what he did with his - might be worth contacting him as he may have them to sell still - that way you get it lowered but have a reasonable ride