The more I've read of this thread and the one immediately following, the less I'm convinced of the rightness of my original assumption that Willoughby is simply the pits, whereas Wickham has to move up to reach that exalted level.

So, actually, the answer is "no" - certainly not any unambiguous examples. Enough has been said in this thread to convince me that, at the very least, his every word can be read highly unfavourably, as the utterances of a narcissistic, utterly self-centred, even vicious man. The inadequacy and offensivesness of his attempts at self-justification - his attacks on the Colonel and Eliza, among others - go a long way to counteract any impression of geniuneness that his protestations may give.