Quickest bang for your buck performance-wise is getting a tuning module. BurgerTuning makes the JB+ for the Cooper S N18 engine. Takes 5 minutes to install and will net you around 20 hp. They run $300 retail, but can easily be found used on some other forums. I had one on my Countryman and it made quite the difference.Thanks for everyone's advice. I think I didn't make myself clear.
I love the appearance of R, it's really classic and fun.
As to the performance, I'm considering how to improve it.
What can I do to improve the performance under the hood?
I've thought about change the intake system or ECU remap. What's your opinion?