I do not believe users that come to SE to answer should be here to farm reputation. If they are, it is for the wrong reasons. What is the goal of StackOverflow specifically?
It is claimed we value reputation but what we do is programming. That's all we do here. Anyone putting reputation above programming is in the wrong field. Gamification is just a way to encourage the process of sharing information.
The OP does have the power to reward up to 25 points to a user. Now think about the following
- How many times did the OP visit the site (Not how long he was a member)?
- Did he/she read the FAQ (Check for analytical badge)?
- Do they know how to up vote and accept answers?
- Do they know that accepting an answer does not necessarily mean it will be upvoted automatically?
- Is English their first language?
All these questions and more tie into how a user responds to answers. And that's what helpful comments are there for.
Is the person defeating the purpose of participating in the site?
Knowing that the goal is to spread information about better programming. I would say no.
Is he using all the features of the site?
No, but it doesn't matter. No one should force them to do that. As the goal of better programming by spreading knowledge has been established by the OP and users who answer.
There are edges, tags where activity is low
Is the responsibility now on the OP to reward users since there is not as much activity as on more popular tags? No, not at all. It's a community we all run the site. So the responsibility is on everyone to vote if there is an answer that is useful. If the answer is indeed amazing I will bet you it will be voted on, it may not be today, it may not be tomorrow but somewhere along the line, someone from a Google search will hit the question and see you answer and say
Hey, this user helped me out let me give him a +1
Boom, the system works.
So maybe this is where the true issue lies... how to deal with low activity tags.