The Slate article makes the forceful case for yes to both a and b.
On the justified question: I think it is fair to draw a line between Romney as "successful business man and job-creator" and "successful investor." The latter is a different animal and one that is not based in doing what's best for the American worker/economy unless you're going to give the "Greed is Good" speech. I also think, on the question of Romney's wealth, it is fair to ask "What has he done with this fortune." If you are running for office and you are loaded, its fair to say "What choices have you made."
I'm not as sure on the smart question. It feels like a hard one to present without being disingenuous. I'm not in love with the latest ads on this for example.