Hey MAX..
Forget nismo...too expensive and everyones got it, its nothing special anymore! But yes theyre right abt it re-selling well on ebay.
I suggest buying a well heard of exhaust ..but something that sounds and looks different! Maybe HKS power ($650) or Apexi N1 dual (£450) exhausts, these sound the best and get them easily in US.
Think abt weight reduction vs power ..true dual exhausts have more power but heavier..i prefer sticking to the lighter ones even if u dont get full power (350z desperately need to lose some weight!)
Remember always try to negotiate postage prices..99% of times they can afford to give u a discount from US!