aggregator offer something unique: A filter to worldwide news/entertainment/opinions The more user the better the filter. Better in the sense that most of the population will consider said topic/news/etc important/entertaining.
The more user means also, the more hidden News/URL someone may put in front of the most people.
More users means also more people to share opinion, advice, etc.
That's how Reddit became the juggernaut.
Hubski SEEMS to be build with another paradigm: a few people having a more informed/interesting/worthwhile opinion than most of us. It sound pretentious, but it's a solid paradigm: Billions of flies eat shit, that's not a good reason to taste poo. So lets follow the better of us. Revenue part. In case 1 (Reddit): the content is users made. the more users, the more link, comment, content, adequacy.
In case 2 (Hubski): the content depend on a few "better" users What you address is the case 1: Getting donation and Selling user info to advertiser. With your only concern being having the most users possible. The day you become second in users base (Google+ Vs Facebook), the site is as good as dead. I guess in Hubski case you should consider totally new solution. I have no fucking clue. But your concern SEEMS to be about keeping your 'better" users. If (names totally invented:) Klein, NewGreen, mkay, Insomnia, refuge, 8bitsam, etc disappear from the site, you'd better get some good people to replace them. That look more like a Twitter model (if Celebrities all leave Twitter, the site is as good as dead)
So I have no opinions on the subject. That's just how as a user I came to see the aggregator system.
Bottom line, in any aggregator (just a most streamlined forum), the users are the only value (some forum present info more easily, have better readability than other, that's the only intrinsic value.)
But the best ever built forum is worthless if empty. And it hearth wrenching to watch aggregators site shamelessly feed of its users. But hey, I get it, the more users, the more value, the more servers to pay for.
What I wish for is a non-profit Reddit. Sell users info, take donation, put ads as much as you want, as long it's just to pay for employees, servers, bandwidth cost, and not to pay shareholders.