I think non-resident property owners do have a right to speak (not vote) at town meetings, or any other sort of town meeting (ZBA for example) if public comments are opened. It comes under Due Process, not 1st Amendment.
So, for example if a town ZBA was discussing a rule that affects waterfront property owners... all waterfront owners (resident or non resident) would be able to be heard (if public comments were open)
https://www.nh.gov/osi/resource-libr...c-meetings.pdf
Woodsy