Yes, Unnati is right - it's going to be too much spamming.
As for giving out points, on several RP sites what they do is let the teachers of particular subjects give out points according to the grade you got in a particular topic.
We can have a particular topic in which the Mods will post saying, "10 points to (insert name here) for (insert whatever)"
There are many contests on IF-HP - the avatar contest, fanfic contest, i_luv_jay_sean's tasks, Guess The Member, those kinds of stuff. We can give out points to the winners. We can also have a certain criteria - if you start a topic that's thought-provoking and discussion-inviting, you can get some points for your house. If you post a particularly intelligent answer, you get points. Stuff like that. Let's brainstorm.