There are 2 reasons they have marketed the Outbacks & mostly wagons:
1) Subaru is a niche marketer by their own admission. They actually created a niche with the Outback.
2) The Outback/Paul Hogan saved the company, there were plans for Subaru of America to shut down in 95, the Outback was launched as a last ditch effort to get the company rolling again.
I don't think they need to do any less Outback ads, I just think they need to advertise more and throw in some of the other models they have.