Most people who've read this book don't seem to realize that there was a reason why so many plot threads were either left unresolved, or introduced fresh. This was the case with Courts of Chaos as well (book 5 in the series): Amber won the war, albeit at a terrible price, but there were far too many unanswered questions.
The reason is that Zelazny was not intending this to be the end to the series, just to this chapter of the story. It is not a well-known fact, but Zelazny actually wrote five short stories that pick up after this book end (they were published in various magazines and, to my knowledge, have never been collected or even made easily available). Those five stories deal with what happened with Luke and the Pattern (#1), Merlin meeting Rhanda (#2), Frakir, after she got herself freed (#3), and Corwin making his way to Amber on a blue, shape-shifting horse from the Courts (#4 and 5).
In those stories, it is revealed that spikards are sentient, Grayswandir and Werewindle are not swords at all, but instead changed spikards, a new race of beings - the Shroudlings, who live in the world behind mirrors - is introduced, and Castle Amber is alive and taking part in things.
Zelazny was clearly bulding up to another series; unfortunatelly, he succumbed to cancer shortly thereafter.