[Mim]

Well you did mention wanting to keep the car easier to drive in traffic so I assume you are looking to improve performance and not mess too much with its daily driver appeal ie NVH levels and ride?

I'd research some basic weight reduction ie removing the spare wheel or switching it to a space saver, if you have a full size wheel in the boot (like my BRZ does). I hear switching the battery out for a lighter one is a good move too.

Then look to the drive shaft, as you mentioned, but I was thinking of an aluminium one rather than CF. You mentioned they rattle? First I heard of this and CF ones are a good deal dearer and not much lighter.

I'm a big fan of upgrading the FD ratio. That speeds up each gear like a 4.556 makes each gear roughly 10~11% faster or so.

Then look to lighter wheels / tires and possibly coil overs with a bias towards better ride (more of an NVH impact).