1. Is tyre roar on the motorway obtrusive and annoying? (I do 40 miles of motorway driving every day for work)
the noise from outside and tyres will be heard in the cabin more than your current BMW
2. Is the clutch weight too heavy in stop-start traffic?
depends on the car, some have replaced clutches (eg exedy clutch) and they can be just right.
3. Is the Bose Stereo any good?
not great as it is a clarion headunit with bose amp and speakers.
4. Are servicing costs reasonable?
pretty reasonable if you don't go to nissan.
6. Is build quality good? (no rattles/squeaks?)
Not as good as your BMW but not really squeaks or rattles
Try probolt, they will charge you half the price of the sun but they are a top quality product and you will get hold of exactly what you are looking for 95% of the time. If you want a good deal find a local nut and bolt place / engineering shop and ask there.
For sale, oem pre 06 air box with used nismo filter included.
Now upgraded with a Post 06 velocity stack
viewtopic.php?f=38&t=50496&hilit=air%2A+box%2A
I'm looking for £85 +p&p
don't know how many miles the nismo filter has done, it's a bit grubby