Great to read your views and i think i have an idea of your age range but sadly for me i could be your very very elderly big brother if we were siblings.
Glad slick50 works for you but what engine oil do you useand i have done a little research into oil additives and find big claims for amatech engine restore but dont know anyone who has used it.
If you are happy with the grounding kit then great but as for slick 50 i personally would keep away and of course then there is amatech engine restore so the oil addatives issue is a minefield but i am interested on you opinion on slick 50 etc.
Probably cleaning the earths was beneficial if they were high resistance but each to their own with the grounding kits and in my opinion it is all in the mind but the mind.
If you are worried about fuel consumption then forget a petrol impreza in my opinion as you buy a petrol impreza for the fun of driving and not fuel economy.