I think it depends on your set up already on the X or if you plan to do anything else later.

Eg if your running standard spec wheels no body kit etc then it can look odd IMHO.

I did it with my old one but it had a full ACS body kit exhaust suspension and ACS 22 wheels and I think it really made the car look much sportier.

On the E70 I think if you have the 21s and a body kit then I would say yes it would look sportier. I did take mine off for a look and I liked it....

As for xmas trees - buy a plastic one in a box or get it delivered !!