On one hand, I think resteeming does increase visibility. As I understand it, if I resteem a post that was published six hours ago, it appears as "new" in my followers' feeds.
That said... it also seems that a LOT of people are only interested in original content. They are less likely to click on a resteem than someone's original post. I also know that when I check out someone's profile and see that almost everything there is resteems rather than THEIR content, I'll most likely pass on following them. So I would use it pretty sparingly.
The only exception might be resteems that are helping a newcomer with their "introduce yourself" post.
A wise answer. Thanks for this post reddragonfly.