(1) Forget about why they use it; anyone who uses anything other than the bundled browser is likely to be more experienced than the average user. Heck, anyone who so much as changes their start page...
(2) Why would you think that? My guess is more, much more. This Opera user probably spends more online than offline.
(3)(a) I might have clicked a banner or two when I had the free version, but there was not a lot of ad rotation. A person can only click on the same advertisement so many times.
(3)(b) Safe? Compared to what? Every time I am forced to use IE, I feel like I am walking down a bad alley late at night, trying not to get mugged.
(4) Webmaster/geek stuff is a good guess. Heck, even if you don't have a record CTR, you might reach a few opinion shapers. Let us know if you try it, especially if you are running webmaster/geek stuff.