if it was a case of buying from scratch and never owning the zed i'd possibly go for the 70, but now i have the 50 i wouldn't upgrade to the 70.
i'd meld the 2, i'd keep the 50 exterior, and put the 70 innterior in it.
for me now, when the time to change comes i'll move on to something different. nothing against the 70, but i like to change to something completely differeetn when i move cars. never bought the same brand twice.