I think high-paying keywords are in boring niches... LOL! My opinion. I'd go for middle ground keywords instead. Yes and something which you know a bit about. Imagine I don't like writing LAW and having to write LAW just for the sake of the keyword.
Wow. Create a blog and post duplicate-content articles about ALL the high-paying keywords. That's a hot idea. Making any money?
You need those blog entries to get to the top of the SE's for it to make you any money from their big $$ ads.