If this change is made, the karma multiplier for a discussion post should also be increased. Right now making a 10 point discussion point gets you 10 karma but making a 10 point post in Main gets you 100 karma. Which doesn't make much sense given the reality of how Main & Discussion are being used (virtually identically: basically you post to Discussion if you're a person with a humble disposition). I'm in favor of having a solid multiplier for discussion posts, 4x at the absolute least, to encourage more toplevel posts. I would also disable downvoting for users with less than 100 karma to encourage more contributions... Less Wrong is such a dinosaur at this point there's little reason not to try this kind of radical change.
I would like to combine your two suggestions like so: Posts in discussion still earn 1 karma per vote. But as soon as a post gets at least five or so points it transfers to promoted. And then you get 10 karma per vote the post receives after getting promoted.
Posts in promoted are visible to people reading discussion, but readers can choose to see only promoted posts.
That way you have a smaller downside risk (if your post is received poorly you only lose one karma per downvote), but you can still get more karma if you write a substantial post that people like.
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.
Notes for future OT posters:
1. Please add the 'open_thread' tag.
2. Check if there is an active Open Thread before posting a new one. (Immediately before; refresh the list-of-threads page before posting.)
3. Open Threads should be posted in Discussion, and not Main.
4. Open Threads should start on Monday, and end on Sunday.