Which 5 series do you have?
There are some truly hideous looking stylised ones out there so perhaps we look at those so we know what to avoid.
The E39 is pretty bland to look at. Timeless and classic perhaps, but still bland in my opinion. I can't be bothered to do anything about it though, I quite like blending in.
E34 and E60 are probably more striking anyway but as a result will stand up better, in my opinion, to some style changes.