Rebuild your stock shifter so it doesn't feel floppy.
Good idea on the switches, do you find stiffer springs at the hardware store or double up on stock springs?
If you have rattling plastic in your interior, use felt-backed tape like some car manufacturers do to kill rattling noises.
I also changed all the bulbs to LED and retrofitted LEDs onto the 3rd brake light.
350z seats are great, they are comfortable and they hold you quite well.
I also redid the door inserts in leather and the back seats in leather + new cloth.
Also made a new deck out of thin plywood since the stock one was falling apart, then I covered it in suede. Covered the headliner in suede too, stock material was ugly.