During braking, accellerating, cruising....where does it do it?
Yes. Get one now.
All cars do it mate, my Stagea was the same because it used to rattle and buzz whenever I travelled down rough roads - it was worse in my car also because I had Tein Coilovers which were fairly firm, your teeth fillings would fall out if you hit a big bump.
We'll need pictures for this one but i'd suggest you rock on down to Supercrap Auto and get some Mcguirs metal polish for the gear knob and surounding console.
1200 does seem a touch high, should be around the 800 mark. Try resetting the ECU by leaving the battery D/C'ed overnight. Failing that - (GTR owners!) Does the throttle body have an idle adjust screw?
I wouldn't bother - if you're going slower than your speedo suggests atleast you'll know you won't get done for speeding any time soon.
Overall it's a very nice example, i'd still be happy with it regardless of its discrepancies.