hey. you've got a 350 z, forget the' GT' bit.
the Bose system as every one knows ain't that great, the rays were an option on early cars. and lets face it every body's got there own ideas on wheels to make the car individual, who uses Cruise control these days with most roads grid locked !! electric /heated leather seats,this is probably the only item that most people want. so instead of re trimming your seats , buy 2nd hand and fit ,yes the heated part is going to be the problem. But the elctric part should be ok, and if not a auto electrician can easily find a fuesed power source .
seats can be sourced between £300-400.
as already stated cloth seats hold you better and are cooler in the summer etc, your z will also be quicker as the base model is lighter no electric seat motors and no sub
as they say there's an ASS for every seat, people who want the perfect car ie colour/alloys/leather / mileage/mint condition etc etc , will have along wait, for me it would be condition/ milage first the rest can be changed ie seats/hi fi/ wheels