I upvote about 80% of comments on my stuff. I don't upvote obvious spam. I don't upvote things like "I liked it lots plz read and upvote (link)". I don't flag that either, but if it's about something totally unrelated, I do.

I feel upvoting comments feels good to people but I do it NOT out of obligation but active desire to reward. I'm ok sometimes having weak vote power as a result. It's not about the money - people see the upvote and know that I read the comment and it's a connection thing.

But the moment it's an obligation, that is gone. So you are definitely not obligated. Do things your way - that's what matters.