If you want to see crap negative campaigning, take a look at slime on Obama.
Grover Cleveland, in the 1884 election. (The smirking “Gone to the White House, Ha! Ha! Ha!” tag was added by Democrats after Cleveland won it anyway.)
I’ve started several posts along these lines, but asking a politician about negative ads are like asking a carpenter about a screwdriver. Some jobs don’t require it, some do.
Attack ads help draw distinctions between candidates. What’s more, they draw understandable and memorable distinctions.
When are negative ads not appropriate? In some parts of the US, there may be sensitivities to different things: in more traditional states, it can be a risk for a male candidate to attack a female candidate too strongly. Other places this isn’t an issue. I’m not sure there is a blanket rule of thumb for when negative campaigns work, I think it is a matter of understanding what issues resonate with voters and how a campaign can exploit those issues to their advantage.
You forgot one: You also want to discourage your opposition from going out to vote. This can be the most effective means for negative campaigning to work.
The quick and “dirty” answer is: Yes, it always works. Unfortunately, sometimes your negative ad works best for your opponent. 
In other words, they can backfire.
No I don’t. Palin a deluge? She was a nobody that the repubs dug up and offered for VP. I can not image a rank unqualified outsider walking into the Vp slot and get a placid press. She got plenty of good press from Fox.