So I'm thinking of getting a BOV because I'm like a 6 year old and it sounds cool!

Performance gains is not my priority as these things don't really make a difference, BUT they sound cool!

So should I get one and how difficult is it to install it and then remove it when I take my car in for a service?

Thanks ;)

Change your CAI out to a Alta and it will open up your stock BOV.

I live in California, how quick can the CAI be swapped back to OEM so I can pass smog?

I live in California, how quick can the CAI be swapped back to OEM so I can pass smog?
Avoid the hassle ... fit the air box and filter from the following:

RealOEM - R56 Cooper S John Cooper Works Tuning Kit (http://www.realoem.com/bmw/showparts.do?model=MF73&mospid=50031&btnr=11_4152&hg=11&fg=95)