I believe everything we do on here has an impact. Anything of quality helps move this site forward and has a compounding effect.
A comment helps to lengthen a post which will help the Google rankings. Also, someone could pull up the post down the road and learn something from the comment. We also gain followers which can help out own posts. Finally, any money we receive can be powered up and help each person we upvote.
It all compounds upon itself.