Absolutely yes we should be cleaning up comments, I've been doing it on occasion, but not as much as I've should yet
There are 3 different situations.
- When most/all of the comments are yours and no longer relevant, delete them
- When you see a long comment chain that is about the on/off-topicness of a posts,
- Open a meta question (and it can be helpful to capture some of the discussion in the question)
- Leave a comment to direct further comments to meta (linking to the new meta question)
- Then finally flag for a comment clean-up1
- When the comments are just non-constructive noise and don't contribute to the clarity of the post (or don't offer the OP any reasons why there might be close votes or downvotes), then just flag for a comment clean up1.
1 - Flagging for a comment clean up is pretty simple, just click "flag" under the post and select "other". Then describe in simple detail what you think needs done and why. Don't go overboard on the explanation, but try to be specific. The moderator who handles the flag might not agree with you, but by providing enough detail you prevent them from misunderstanding why you believe the comments are no longer relevant.