I think there's no harm in adding them, some people may use them even if they are just a reminder to share. I think they should be kept fairly simple though, no JS etc.
I'd agree - except for the tracking behaviors that come with the most common solutions - copy paste a line of js, or enable a plugin that has the same js, etc.
Simple self hosted share links that were just links would be reasonable, but it seems not many take that route.
