I agree with issue #1, but the other solutions (minimum karma of 100 or something like this) would have the same problem. Regarding your issue #2, I think users with negative karmas would have to be disallowed submitting in order to stop spammers.

"just overrun with relatively well intentioned people who don't know what's appropriate."

Basically my idea was that you have to prove you know about HN-culture by writing good comments, and then by gaining karma you can start submitting.