I would say that upvoting comments is a good way to motivate people but its still not what we want. We want people to be more active on content that they enjoy not because they can earn some $.Well yes it is a nice bonus but sadly people are upvoting comments less and less these days (and for a smaller percentage!) - I always upvote people who comment on my posts (aslong as it it related to my post) as I think they have spent the time to come and comment and engage with my content.
Yes we want people here to engage for the fun of it without rewards being the number one factor - I generally engage with the same people alot on here -maybe I should expand out a little bit