Excel, haha..same like me at 1st. The girls don't understand why we mod our cars same like we don't understand why they always need to do their hair, nails, make up, having more than 4 pairs of shoes or facial.
What I did was try to go into her 'world'. You know mix around with her friends, saloon colleague, her boss..go with her to beauty exhibition (my girl is a beautician) ask her about her opinion about the beauty products or slimming products in the market. Try to read some female magazine (It helps you know more about the opposite sex)
I also try to talk to my girl about cars. She don't like cars at all in the beginning and can't understand why we spend so much money on the car. As time goes by, we exchange information bit by bit then she starts to know more about cars and know how to appreciate. This does not mean you can spend all your money on cars. My girl now also told me I can spend on cars but when only we have extra money after settling all the important things 1st.
She now even eying on M3 and M5....

and have more interest in cars and would go to SuperGT with me even she knows it's hot and sure will get burned.
What I suggested might sound weird or gay to some but it work out for me as I find that I have more to chat with the opposite sex and they won't feel boring.
Girls don't like guys keep talking about their own story and stuff to them so does we (don't like them keep telling us their hair,nails, fashion..etc. They love to have a conversation with you rather than you telling her story. Well if you have gone overseas or interesting place they will be very happy to hear your experience because most girls love to travel.....
If always talk to them about cars or always cars cars cars. They will find you very boring and self centered because to them, in your eyes there's only cars. If anything i can help let me know.
Bro, don't angry what I've said. I'm just speaking out of my experience and what my girl told me.
Just take this as an example
Guys Girls
Greddy = Gucci
HKS = Prada
Apexi = Chanel
Volk = Burberry
We spend Rm400 on a set of exhaust will be same like they spend RM400 on shoes, clothes, hair..etc.