"And, as with watching birds or going Paleo, talking about the material purge is just as important as actually doing it."

The implication is that, like your friends who "went Paleo" or your CrossFit buddy, bird watchers will...not...shut up about it. But I don't think I've ever known a single person in my relatively long life that would go on and on about bird watching, so I don't get the comparison, either.

I don't personally agree with the author's point, or the article in general, but my reading of that sentence was a suggestion that all three are things that the practitioners talk about at length. Each is a lifestyle choice or hobby that people like telling others about. Another example is CrossFit.

While I disagree with the author, I believe his intent was to claim that bird watchers, Paleo dieters and minimalists are similar in that talking about their respective activities is just as important as participating in it.

  "And, as with watching birds or going Paleo, talking about [minimalism] is just as important as actually doing it."