My understanding of the way money in TV advertising works is that the most-desired demographic is young men -- and I can imagine that SPN was deliberately gendered to appeal to men as well as (or even rather than) young women.

I don't disagree with anything you say here; persobnally, I think a number of the guest stars (both male and female) "come to life" as individuals (even though I think many of them also do serve as symbols or motivators for Winchester family drama.)