Yes to pretty much everything you said about Anya and Wesley (have only seen up to season 3 of Farscape and the others not at all, so I can't comment on those). I loved Wesley to the end, but I remember feeling this pang of irritation when everyone started fawning: "Oh, he's good enough for you!" *grin*

And yeah, Anya/Xander was Not Good in a way Cordy/Xander, for all its hate/love, never was.

I think one reason Anya was so much readily accepted than Wesley, apart from the VERY different ways of departure for Cordy and Doyle, was that she had already started making a place for herself in the series by the time Cordy left. Wes was a previously known character, but from BtVS, not Angel. If he had been recurring in the early eps, like Kate was, I think it would have been at least slightly easier to take than "Here's your new regular, enjoy!"