I agree that "whether polyamory (or cryonics, or whatever) is a good thing" is a thing we want to know. Possibly even the thing we really want to know, as you suggest.

When you unpack the question in terms of improving lives, benefiting people, etc. you're implicitly adopting a consequentialist stance, where "is polyamory a good thing" equates to "does polyamory have the highest expected value"? I endorse this completely.

In my experience, it has a high positive expected value for some people and a high negative expected value for others, and the highest EV strategy is figure out which sort of person I am and act accordingly.

This is very similar to asking whether a homosexual sex life has the highest expected value, actually, or (equivalently) whether a homosexual sex life is a good thing: it definitely is for some people, and definitely is not for others, and the highest-EV strategy is to pick a sex life that corresponds to the sort of person I am.

All of that said, I do think there's a difference here between unpacking "is polyamory a good thing?" as "does polyamory has the highest expected value?" (the consequentialist stance) and unpacking it as "is polyamory the a characteristic practice of virtuous people?" (the virtue-ethicist stance).

Perhaps what I mean, when I talk about markers of virtue, is that this community seems to be adopting a virtue-ethics rather than a consequentialist stance on the subject.