You have $10k USD and a stock BRZ...
 

Not for stance!

Go... :burnrubber:

(Parts/build - not investing, other car or track days)

Is the car paid off?

Supercharger and wider wheels

Of course :). It's "your" car.

I'm already over $10k USD on my BRZ in mods.

Tires and track days.

In that case, OEM crash bolts, an alignment, a helmet, and seat time at an autocross or at a track with an instructor.

It's a very capable car out of the box.

Hookers and blow

Valenti's and 9,700 tacos

Hks coils (1700)
enkei gtc01rr (2k)
Yokohama ad08 (800)
headers plus tune (1500)
bbk (3k)
bride seat (800)
weight reduction (free)

Option 1:
Sound generator delete.
Camber bolts.
Alignment.
Tires.
Brake pads/fluid.
All of the track/autocross days.

Option 2:
ACE header.
Tune.
WEDS TC105Ns in 17x9.
RE71Rs in 245/40/17.
Brake Pads/Fluid.
Oil cooler.
RCE Tarmac 2s.
Raceseng CASCAM plates.
SPL LCAs.
Alignment/corner balance.
Front sway bar.
Whiteline Roll Center/Bump Steer correction kit.
Rear subframe/diff bushings.
Sound generator delete.
Track/autocross days.

I'd drive the BRZ as is and find a 1959 Austin Healey Sprite or a Kaiser M715.

Dude, too funny. This is exactly what I said to a mate this morning regarding my tax return.

Invest in taxable account for my next ride in about 5 years or so.