Not knowing too much about the skyline i'm coming from a biased view, however you should choose to do what is practical for you! Yes being a zed owner i can say that it is expensive for parts mostly because if u can't get them second hand they need to be imported from jap. (pain in the butt). Having owned my tt zed for 2 years now, regular maintenance aside, i've only spent about $1500 on repairs, mainly a new heater core. Regarding issues on repairs the timing belt to get repaired doesn't need the engine out and the little bypass hoses are a pain to fix. Therefore if you choose the z be prepared to put a little aside for hidden problems. Thats my view anyway, either would be a good car but think what u need it for. Happy driving.