The karma of the submitter has no effect on how a story is ranked. Nor I suspect does it affect whether people upvote the story, except when the submitter is one of maybe 100 HN users who are well enough known that their username as submitter makes people pay attention to the story. Plus if we noticed anyone consistently rewriting titles we'd ask them to stop and eventually ban them if they didn't.
The key point is that good stories can get lost in the noise and once lost reviving them is very difficult. Re-posting the story with the same URL just adds a karma point to the original poster but does not get any mention on the "new" page so no-one else gets the chance to review and (possibly) update a good but overlooked post.
Do people really care about karma and try to get karma by posting good links? I guess it works too, but 99% of my karma comes from writing smart comments (hopefully), which is quite valuable to the community too (I hope).
I saw your post and was awesome but have little upvotes, then i entered and it was the same but with a lot upvotes, pretty strange . I felt a little sad because you deserve some good upvotes man.
There is an awful lot of interesting content that gets bumped off the "new" page really fast. I think stories that get upvoted on that page should be able to percolate longer before disappearing.