I'm seeing a phenomenon wherein questions receive multiple answers that are very similar in nature (for example, the 0.9999... = 1 question) or answers that do not build off or acknowledge the existence of other answers very well. The first case, at least, seems like something we should discourage in favor of upvoting. Do multiple redundant answers seem like a problem to others? If so, how might we address it?
For questions such as the .999=1 that you mentioned, that receive a ridiculous amount of marginally different answers (or answers that are posted simply to add one or two thoughts to one previously posted), I think the best response is to make the question community wiki and users can help to combine the many anemic answers into one (or more than one) comprehensive answer. There is no good reason to make people scroll all the way down because someone posted 3*1/3=1 and someone else posted 9*1/9=1. Combining these answers and adding some explanation would best serve the ultimate goal of having an well-written answer to the question that people can refer to later.
Multiple redundant answers are annoying and seriously affect the usability of the site. You can't find the other answers if all the answers are the same. However, one or two duplicates isn't terrible and as sepp2k says can't really be avoided.
I think the solution is downvote duplicates that aren't roughly simultaneous. Or even flag them for moderator deletion.
I'm interested to see what users of the trilogy sites think. This same problem exists there, but I don't think there is any dedicated method to stop it.
In fact, I'd wager it's not a big deal. So what if there are 10 answers? People just looking for the "best" answer will be looking at the first answers anyway.
From my experience on StackOverflow, this tends to only be a major problem with community wiki poll questions. It is slightly annoying on other questions, but not a major issue