I may have spent more than 10k for tires only
But I wouldn't say tires, brake pads, other consumables as mods, because they may get more expensive on other platforms and you will be needing to change them.
Also, the 370z is a more refined car compared to 86, I drove both, I drove both stock and modified, stock 370z is more capable compared to 86, you only needs to get camber in front to unleash its potential, the alignment is very conservative specially front, on other hand, I would agree 86 will make you push your skills, but it doesn't give exciting feeling when I drive it.