It's all been said, but here are my two cents anyway:
I'm definitely with Marty there. Poor connections have a higher resistance (loose, oxidised, whatever...), and that generates heat. When it gets bad enough, the connectors end up looking like the ones in @droydx's photo. In most cases, the problem is exactly that: the connector has just gone bad. Repair it (and maintain it in the future), and the problem is solved.
No.
Yes. If there are spikes, the regulator has a problem, at least as far as I know.