Personally, I wouldn't do this. I think the 6 series has a very nice line, and adding spoilers on the boot or the window breaks that line, especially in side view.
But then again, thats my opinion, and since when does that count
About the chip, if you dont want any hassle with BMW, just wait to do this until the car is out of warranty. It'll make your car feel "new" again, and no worries about BMW giving you the finger in case of car problems
I wouldn't go all the way on body kit, too much IMHO, but I was thinking of a rear window spoiler. Very subtle and I think it comes in carbon.
As for the chip, my current thinking is to wait until most of my warranty has gone. Trouble is that's 2.5 years. Will I keep it that long, who knows. I said I would keep the Zed for a few years but ended up selling after 13 months.