Looks like Stack Overflow risks the same descent in to mediocrity that plagued Yahoo! Answers. This is the problem with points systems: people will game them, often to the detriment of the site. None of these tips involve actually providing a good, useful answers. Compare with Ask MetaFilter, which provides excellent quality with hardly any game mechanic - instead using community norms to keep the quality high.
It is inevitable that any Q&A system managed by the masses versus a knowledgeable few will descend into mediocrity. The harder the question is, the fewer people will vote on it, and even fewer would be qualified to vote on it.
Having said that, I think Stackoverflow does a reasonable job of coping with it, but abuse still goes on. I only first noticed these tactics when they were used against me. Without naming any names, I can tell you that many of the people with 15k+ rep have used these tactics.
The only advice that really worries me is the advice to downvote competing answers. Getting votes for providing quick answers that you then refine is not a bad thing. But I think Jeff and the team may need to prevent people who've answered already from downvoting other answers, otherwise you could be right.
No, it IS a bad thing. What you get (and what happens on SO) is that certain people will post something, anything, to new posts so they have the first comment. They then spend the next five minutes gradually expanding their answer either based on their own knowledge or worse of all, by cherry picking info from other peoples answers.
This is certainly not the case with every answer, and it it may be more prevalent under some tags than others. However it happens enough that I've become fed-up of crafting well thought out replies just to see them copy+pasted, with some minor word changes, into answers from first-posters.
To be honest I don't see that as a problem; first, the people answering a question are the people who are more likely to come back, read other answers and possibly downvote the very bad ones. Leaving negative comments is very obvious too, you won't get too far with that. Second, it never happened to me (and I've spent way too much time on SO), never seen it happening so I suppose this can't be too widespread.
