I am not sure what the rules were before but don't you need to actually post to get points?
Yes, you earn points thru posting.
For topics started = 3 points
For replies to a thread = 1 point (usually) but admin can upgrade it to 3 points if it's constructive
If you create a topic that is only one post. Would it not be better to create a topic and constatly reply to it? That would help you rank up very quickly while actually participating in the forum and in your topics.
Ideally, yes it is better to respond to replies in your own thread. Not only you are gaining points and activities, you also get to interact well with other members. But from what I observe and what I experience so far, some thread starters do not respond at all for some reason. In my case, I usually respond to questions and points that I have not raised in my original post. Often times, comments are just repetitive.