(Note: I've summarized my points at the bottom for easier reading)
Is an "I have the same question" message even appropriate as a comment? To me, this seems like it might be equivalent to an up-vote on the question. However, since the site will most likely be set up to not allow 1-rep users to cast votes either, this doesn't really address the underlying issue of allowing such a user to provide this feedback.
- Perhaps their vote could instead go into some kind of "purgatory" where it doesn't count until they actually gain enough rep (1). At that time their votes can be released from purgatory and counted.
Granted, an up-vote doesn't necessarily mean that the up-voter actually has the same question; they could simply be interested in the question, but does anyone care about that distinction?
- If a user really wants to say "I have the same question" instead of simply up-voting, then one possible idea would be to introduce a feature to allow a user to optionally pick a value from a drop down list to accompany an up-vote or down-vote (2). The values of the drop down list could be something like the following:
- I have the same question
- I am interested in this question
This would allow users to effectively say "I have the same question", but would not provide them with a free-form text input that they could use to spam.
If a 1-rep user simply has the same question, then they can cast a "purgatoried" up-vote with the appropriate option selected from the drop down list. That way, if someone really does care that so-and-so actually has the same question then they could potentially see the list of users who selected that option (3).
Else If a 1-rep user has a similar-but-different question, they could just create a separate question so that they can explain the difference; I don't think that's a great solution, but I think it's more appropriate than leaving a comment. Perhaps a way to create sub-questions or to relate questions together would be a nice feature (4).
What if a 1-rep user has more to say? Well, then perhaps those users could be allowed to comment with the understanding that their comments will go into purgatory until they gain enough rep for their comments to be seen by other users (5).
Regarding "Thank you, this works" comments, I think the same argument applies unless the comment is coming from the original asker of the question. Can a 1-rep user can leave comments within their own questions? If not, I think they should be able to (6). EDIT: as Grace Note pointed out, yes a 1-rep user can leave comments within their own questions.
Similar to the point above, if a 1-rep user only wants to say that an answer worked for them as well, then isn't an up-vote sufficient? Similar to above, an optional drop down could accompany a vote with values such as the following:
- This answer worked for me
- I like this answer
- You are Jon Skeet
Summary of points:
Allow 1-rep users to cast up-votes that go into purgatory until they have enough rep for their vote to count.
Provide an optional drop-down list with common values to go along with a vote so that the vote can be categorized. Such as "X number of users have the same question. Y number of users are interested in this question."
For those users who really care, allow them to retrieve a list of the users who selected "I have the same question".
Introduce the concept of sub-questions or a way to relate specific questions together.
Similar to #1, allow 1-rep users to submit comments that go into purgatory until they have enough rep for their comments to be seen by other users.
Allow 1-rep users to leave comments within their own questions. EDIT: as Grace Note pointed out, this is already allowed.