That's all. There is nothing more to think about while voting. If you think there should be more things to consider while voting, please explain what and why.
I certainly support the heuristic: Upvote = "LessWrong discussions should have more of this." In fact, I've been advocating it for long enough that when I first advocating that interpretation it provoked controversy in as much as some considered it too cynical compared to more pure ideals along the lines of votes being obliged to mean "the point in this comment is rationally coherent". That said, it isn't quite the only consideration that it is reasonable to take in to account and I apply both of the heuristics mentioned above from time to time.
Replies are not necessarily as good or worse than their parents. A lot of the Sequences on this site might be construed as "replies" to more mainstream statistics, philosophy, or science, and yet I would certainly hope that the Sequence entries would get more upvotes than their parents.
I just found out that a new website feature was implemented 2 days ago. If a comment is voted to -4 or below, it and all replies and downstream comments from it will be hidden from Recent Comments, and further replies in that subthread will incur 5 karma points penalty. The hiding, but not karma penalty, applies retroactively to comments in that subthread posted before the -4 vote.
This seems to be worth a discussion post since most people are probably still voting things to below -3 without knowing the new consequences of doing so.