I think you're probably pretty safe as a private individual doing this for fun or as part of red team ops. If you launch a worldwide dragnet for this kind of data and then publicly use that data as part of your commercial offerings, the story changes somewhat.
That case never went the full distance. Google's motion to dismiss was ultimately denied, but the case settled for 13 million; it never went to trial and class members did not recover any damages under the Wiretap Act. As such, the only thing we can conclude is that in the 9th Circuit, WiFi is covered by the Wiretap Act. We cannot conclude from this decision that sniffing WiFi on its own has resulted in liability for damages. That issue was left unresolved.
HN eats the last period; you can use %2E to avoid that.