Almost 4 years after this question, here's how I've been handling it: I go with the wind. Granted, this doesn't really answer my question as I'd like, but in the end it is how I've been doing it.
Main thing I do to "find the right question" is I don't look for them. I just continue with my day to day... When I have a question I mostly google for it. If I stumble on StackExchange I'm glad to find it answered, if there is no answer that satisfies me I add one, if there is no question then I ask one. I hardly ever find unanswered questions, but I think it did happen once or twice. I mostly find those "unanswered questions in need" in more obscure Q&A sites, such as Unity3D or AskDifferent - There's only less than 10K unanswered there, and less than 40K total questions, against 1.7M and 7.2M from SO.
I actually only ever actively look for questions when I see I have less answers than questions, which usually happens when I start in a new community. Then I quest for "questions I can answer", as a way to keep my Q:A ratio closer to 1:1. I don't mind having more answers than questions, what bothers me is taking more than giving. For whatever reason, it just pokes me at night.
So yeah, I haven't used any single resource from all the helpful answers here in all these years. That's not to say I haven't used any tools...
Best tool I've came across was Newt. I think it's for mac only, but it's awesome. It notifies of messages and it brings random new questions as they pop up. I haven't even used the pop up feature, but it is quite nice for finding questions at random. And I have actually stopped using Newt this year in favor of the next one...
Second best tool was StackAlert, which has almost nothing to do with finding the right questions, but it kinda helps me with that as well because it keeps reminding me of old posts thanks to new people interested in it who post up new things. Eventually I look at the similar questions or there are new links or I just try to update stuff and end up finding new questions.
In the end, I've been using a lot of patience and, in one word, serendipity to find the questions.