Spirit Tracks is really not that original. PH is original. ST is a game that focused on improving PH.
XD PH is a game that focuses on improving TWW.
Well, not exactly, since it was on a hand-held and it changed all the controls and even gameplay style, but the main aspects - toon shading, sea sailing, etc. are all there; improvements include a smaller sea, more to do on islands (although fewer islands), etc. Then of course, as I said it's pretty different in some other aspects, but it's far too similar to be considered original. (I haven't played TWW much, but I have seen a lot of gameplay and such.)
As for the poll, I haven't played ST, but I have watched videos and info and walkthroughs etc. From what I've seen, it's not a bad system, but it would need a lot of modifications to be reused. Therefore I voted "It's ok", but I'm not against a similar system - just not too similar.