yes and no. Yes if you upvote a lot, your steem power voting power goes down. You can look here if you want to see your current voting power percent: https://steemstats.com/
For example my voting power is now depleted to 70%
But currently you can vote a lot before it goes significantly down. By the way it needs round about 5 days to regenerate. So yes, your voting power goes down if you write a lot of comments and upvote them all, but as long as you dont write a lot of comments this should not matter much. But so or so because of the exponential payout for posts you only get some significant steem / dollars if also others vote for it. So there is no reason to upvote trivial comments. Therefore i would only upvote comments that either have the chance to get more votes, or you want them to be more visible / displayed in the top.