I guess I'll just touch on the mods side, As far as CEB, and Cold air intake and tune will net you right around 300WHP( See sig), Cost for me was pretty low, The CBE would cost $1000( Mine was way less test fit car), Cold air intake was $375 and tune was $500 so what $1875 so for under 2k you will change the way the car drives and have tons of fun
.. Warranty issues will only come up if you have a tune and a ECU issue, But the UPREV you can switch back to a "Stock" Map if you are going to the dealer for that type of issue. Overall these engines are pretty well made and should have no issue, Yes there are a few but nothing to worry about.
As far as what model get a in between, My car is loaded NO NAV, Honest do not need it ( Smart phones FTW) But have leather and heated seats and Roof( I have a G37). But get the Z and be happy. If worried about the winter get my car G37X Coupe.
__________________
14 Q50 AWD, ARK, ECUTEK (SEB), Takda,