I don't have any marketing data on whether advertisers prefer paying audiences or not, but I assume a lot of that would depend on the advertiser. I know that the bigger players in web media (facebook, myspace, etc) are definitely "bottom-of-the-barrel" when it comes to advertising rates because they reach such scattered demographics.
With that being said, I don't fully understand your point about advertisers preferring paying audiences. I think the problem is in the math. If I start charging for content (turning my users into a paying audience) then I'm going to most likely going to serve less page views. I don't know if the extra money advertisers are willing to spend for my now paying audience would be enough to offset the loss in page views.
The main example of a media website with a paying audience I can think of is the NYT, and I think the only reason they can get away with charging for content is because they've been established for so long. I think the rest of us are going to have to decide between 1) charging up front 2) trying to build a media property 3) trying to make money from premium subscriptions (which usually just amount to being donations from dedicated users).
Thanks for the reply, I'll definitely be thinking about this.
Printed publications make far more per unit from advertising than they do from the subscription fee. If advertisers didn't care about paid subscriptions, it would be in their interest to give their magazine freely to anyone and everyone who wanted it. But they don't because advertisers only care about paid subscribers. That is why magazines seem to try as hard as possible to give you nearly-free (but still paid) pricing on subscriptions.
I don't know why that is, but I know enough about the publishing industry to know it is true.
Nearly all newspapers and magazines are well into the black before you buy them. Consumer research just says we don't value a magazine that's free. (Vice is upsetting this current model)