Comments are an important feature. They are especially crucial to the site, because they allow others to suggest abstract improvements or ask for clarification in answers and questions. They are also the only way to interact with other comments. That means if a link or fact in a comment is outdated/wrong or a link dies, there is no way to point that out as a sub 50/200 rep users. Comments are often the best way to interact with old questions or answers to old questions, that have a high google search rating, but might be outdated or have links to information that was (re-)moved and can be improved by changing the link or information slightly.
My suggestion would be to give new users 1 lifetime comment, and then give the right for another comment 1 week after the comment was made, if the comment is not flagged. If the comment is flagged it's removed automatically. This would require no real moderation, because users involved in a question/answer will recognize spam or noise (like "+1" "thanks") immediatly and flag. You could give this privilege after 2+ rep to prevent account creation for posting spam/stupid stuff.
This would punish and limit useless/stupid comments/spam by beginners until they are more experienced, while still giving below 50 rep users a way to contribute something to a question, where they have something meaningful to contribute.
This would really help new users to point out improvements, errors, outdated information or dead links.
See for further cases where something like that would be useful: