By definition, the level of engagement with a big open (uncurated) crowd will be small. You can only have a “forum” relationship with your community. They may generate huge quantities of ideas that may or may not contain real insight but only a very small percentage will have any value for the client, even as simple media channel “filler material”. (more on the proliferation of "infotainment" content production later)
For the more succinct briefs that require a greater degree of relevant ideation/innovation and finish, tapping the expert crowd is the most fruitful. Both client and platform guide the ideation process.
But if you give both types of crowds the same brief, no matter how large the open crowd is, the amount of successful, relevant ideas produced is very small. That's not really a bad thing. The brief should be so tight that you get a lot of very similar solutions.
Watch any logo contest. (This is the most basic of all CS competitions, and yet logo-design is actually a very difficult subjective process even when you have a personal relationship with the client.) It's a very good petri dish for examining the way open crowds work and think. A logo design is unforgiving. You can judge the expertise of any graphic designer by looking at their logo portfolio first. On the open platforms, everyone can play, but it becomes obvious very quickly who had no concept of design. The playing field may be level, it's all nice and democratic but only those with some expert knowledge of design will actually win.
I’ve said it before and I’ll keep saying it. Ideas come from everywhere and from anyone, the big idea too, but typically that takes more work and deeper thinking. You can crowdsource a logo anytime, but if you need brain surgery it’s best to get an expert. ( I know, that analogy sucks but you get the idea) General, soft content can come from the open crowd, focused and salient marketing ideas come from the more dedicated expert crowd. And of course the payment model is different: it's less of a lottery and in some case all participants get paid.
