My car good be technically finished. It doesn't need anything else...
.... however.....
I want to upgrade the fuel pump to Walbro, upgrade the fuel lines and change to 550l pink STi injectors.
And then, of course, look at the turbo to make sure I'm still getting enough air for all that fuel.
And then, if the engine looks like it might struggle, unlikely, I'd look at forged pistons, rods, etc...
On the inside, new upholstery, new ICE, tint windows, new gear knob, door cards, all the little things to bring it up to date.
On the outside, respray all black, new front and rear bumpers, side skirts to match. A touch of carbon fibre for the bonnet and boot lid & rear wing.