I generally wait until I have at least 5-10x the amount I want to spend just sitting in the bank. Like now, for my $80 pulley. Even though I know it won't hurt me at all to order it now, I'm probably going to wait til the end of the week to order it.
Why tune/mod/throw away money?
The car becomes a part of you. You can't mail-order new lungs to become a runner, or new legs to zig-zag across a soccer field. But you can order an intake so your car can run faster, and new tires so it can zig-zag across a race track.
Plus as your car gets better, you get better. Our reflexes and reaction times are much more finely tuned than your average driver texting and driving. This is from going to race tracks and tooling around on twisty back roads at 3am after you just got done putting on your new springs and want to know how just much better they are.
Plus the sense of completeion and a job well done when you put your motor back together, crank it, and it actually starts! With no leaks, no misfires, no explosions. what a great feeling, no? Or you get done replacing/upgrading your brakes and go for a drive and live to tell the tale? How nice is that.
I love the car culture. I love cars, and I'll probably never stop modding. I don't care if we have to switch to hydrogen, CNG, corn fuel, or childrens tears. I'll find a way to make it faster, better, and more personalized for me.
But that's my story.