This is similar to the thread 90 unanswered questions and counting, I have just tackled and answered 4 unanswered questions - it took a bit of research, but was doable and I think the answers are of a reasonable quality.
Why am I mentioning this?
There is quite a bit of talk about good questions attracting experts, but I believe it is a case of good questions and answers would attract even more - I found this to be true when I used to run a forum (and yes, I know SE is not a forum, but a similar principle exists), that it is good content that attracts new visitors - as with the evidence of expertise in both questions and answers.
Time? heck, I have 4 jobs and I can still do this. The questions I answer are more often than not beyond my expertise area... so are a challenge, but an enjoyable challenge.