Join my club!!! I just convince them that it's going to get better milage or parts will be cheaper if I do this.
"If I put on a cold air intake, I'll get better milage cause the colder the air, the better the combustion." or "I want to get some 15 inch rims cause the tires are cheaper for a 15 inch rim than they are for a 14 inch."
You just need to do things like that.
My next project...
"Dad, I think I'm going to get some KYB AGX series struts. The car is due for them and they are cheaper than stock, plus they are adjustable so I can make the car ride softer(yeah right)."
He hates the way it rides stock, he thinks it's too rough of a ride. He thinks it should ride like my grandma's Oldsmobile.
Good luck...