After how many answers is it no longer worthwhile to add one more?

That’s entirely up to you. It might come down to one of two things. You’re able to articulate a better answer than what has already been posted even though you don’t know it yet or you risk the chance of being redundant. I’ve been guilty of both of these possibilities on more than one occasion.

Never. Keep answering your sweet heart away Madame de la Yarn.

I think you should. I think everyone should. Even if you’re not giving a new answer and you might be saying the same thing as other people… Well, it can still give the asker of a question a general consensus of belief or opinion, which I think is always interesting in and of itself. :)

Some threads stay alive for months or more. There is always something to learn and something to share.

I agree with @DrasticDreamer. Even if your answer is a repeat one, you might say it in a different way that clicks with someone and helps them.

It never hurts to add confirmation.

Funny thing. I have wanted to ask a few questions and went with Google first. First hit on Google was Fluther. Lots of people see what we write here even if they never join.

There’s no harm in contributing an answer, even when others have contributed many before you.

I agree with the above, but highly recommend that everyone who posts to a question requesting factual information read all the preceding posts before answering. Sometimes it’s painfully obvious that this simple courtesy wasn’t observed.

I don’t add anything if someone has already said what I want to say, because I usually stop reading answers when they start getting repetitive. I don’t think “Me too!” adds much.

(Maybe “Agree” and “Disagree” buttons, that keep a running tally, underneath quips?)

Yarnlady, I lurve this question! I usually judge it by whether I think I have something new to add.

If I look over previous comments and feel I’ve nothing to add, I’ll find try to reference someone who said what I most closely would have in order to show support for a question I take interest in.

I think this is such a good question. I’ve been wondering the same thing myself.