It's nice if they'd reply, upvote or thank everyone in a single message, but for all those example discussions it's not important. Discussions where people request or require updating with information is an exception, but enticement doesn't require rules nor exceptions.
I always like to start my comments or replies with a salutation to the Original Poster, that's usually the sole kind of formality I consider, but respect should never be formal- and standardized, because it suffices in personal morality. If I start a discussion I'd like some insightful answers too and it's sensible not to expect any. On the other end, it should be expected that people offer more than answering an inquiry, which potentially attracts conversation. I feel people aren't really open to discuss, if they're not open to converse. To me that openness is an actual discussion, and a debate is really distinctive, that openness requires seriousness and sincerity as well, and conviction the least.