Submission quality is secondary to the drastic decline in discussion quality.
I've always believed that best way to improve the quality of contributions is to make the opportunity to contribute seem finite. It'd be interesting to see what happens if you cap submissions at 2 per user per day and max comment thread participation out at 5 or 10 per day. With a limit in place, people may do a lot more thinking before speaking or submitting.
Maybe bonus submissions/comments could be awarded for some sort of karma threshold on individual items (e.g. One more submission if you hit 50 karma on an item or one more comment if you hit 15 on a comment.)
I've always believed that best way to improve the quality of contributions is to make the opportunity to contribute seem finite. It'd be interesting to see what happens if you cap submissions at 2 per user per day and max comment thread participation out at 5 or 10 per day. With a limit in place, people may do a lot more thinking before speaking or submitting.