I think everyone has to find their own balance on such practices. As you say, there are pro's and con's.
Everything we write is licensed under Creative Commons (I'm sure there's a better link, but that's all I found quickly), so we should all be comfortable that others might reuse our work. But the issue of earning reputation conflicts a little with that implicit permission.
The be nice guidelines are also relevant. Just because two users post substantially the same idea doesn't mean one took it from the other. All sort of scenarios could have occurred.
Practices I've observed
On other stacks, it's common for a user to integrate comments below their own post into it. It happens less often here. The post author usually comments along the lines of thanks, I'll add that in, or just adds the idea / clarification / change and either gives credit in the post or in the edit comments.
So I think the main thing is to give credit. If you give a link that's better, because people can follow it to vote up the work you reference.
A few of my own examples
Here is an example where I've incorporated a comment.
Here is a case where someone else's answer inspired a change.
And here is a case where I link to another comment by Daniel.
The main thing is to behave with respect to our fellow community members. Treat others as you would want to be treated. But also, we should police our own community, using our votes to show approval or otherwise of other's behavior. If you can do it politely, you can also leave comments. Or flag for moderator attention.