I think for the last few books Martin simply tried to re-write far too much.. He introduced too many new faces and totally changed the dynamics of the story and the pace, it was like starting again with back stories and learning new histories - he really needed to have some of these characters (Dorne) in from the beginning.
I do think the whole "Game of Thrones" that we are seeing as the main plot line currently wont be the climax of the show.. The wraiths are the main enemy for me, everything else is a side show. That's why I believe Dany will come to Westeros eventually, the dragons are the key (fire) to breaking the wraiths (ice) hence me suggesting an alligence between Dany and Jon.. A song of Ice (Jon) and Fire (Dany) etc..