This is fantastic advice. I have had lunches like this numerous times. They have been overall a very successful strategy. Sure, you will have a very small percentage that don't really provide insight...but that is well worth the cost. It is often important to preface the invitation with an assurance that you aren't going to try and sell them anything.
Talk to anyone. Preferably, the kind of person who a) has money and b) wouldn't think something like "Hmm, something sucks in life, I think I'll go announce this fact on a social news service in the hopes that someone will solve it for $9 a month."
It really is that easy.
Here's something which will work for anything you care to learn about: "Hiya. I'm interested in your industry. Would you let me buy you lunch so I can ask you about your experiences in it?" Best $25~40 you'll ever spend.