Good thought provoking article but I disagree with this article a little bit.
I think it would be a mistake to ignore broad keywords. Although they tend to not convert as well, the search volume of these keywords compensate for this, and when you target broader searchers, you tend to attract a lot of associated long tail traffic that converts better.
Also, just because a search query is broad in nature, doesn't mean the searcher isn't desperate for a solution. While user intent is specific to the keyword to some extent, it's also your job as a marketer to convince them in your copy through good CTA's etc.
Buyer keywords that are closer to the end of the sales funnel may convert better, but they have fewer searches and they're more competitive because online marketers are targeting these kinds of keywords. It's a lot more difficult trying to promote commercial content.
All in all, I don't think blanket statements like you should only target âBuyâ keywords is necessarily true. IMO you should be be targeting both types of keywords in your content/link building efforts.