Good article. One quibble: $5k for a conference sponsorship is pretty cheap; try finding any space at CES in that price range!

If the conference audience is a perfect fit, and you feel your company/product is far enough along to leverage the exposure, it could make total sense to pay for a booth/sponsorship.

If you don't have $5k to spend on marketing, or it's too early for it to be effective, that's a different story.

But if you do, then compare spending the same amount on AdWords (or other marketing/lead-gen channel X) and see if the math works out.