As for the chrome to black - totally agree, but I'm not sure I'm brave enough to start taking off the body molding on a new vehicle. Maybe I'll think about it more once it gets a little older.
For the question about recalibrating the computer:
The technically correct answer is that you should have the computer recalibrated for the larger tires. This should change the shift points, speedometer, etc... I'm not very familiar with new vehicles, but in the past you would have a scanner hooked up to a port under the dashboard to make the change.
The reality of it is that the change is so small, I never bother with the computer change. The speedometer difference is so small it's almost not noticeable at all and the shifting seems fine to me.
So I guess it's really up to the individual whether or not to make the change.
One thing I did need to change however was the headlight adjustment. Once you lift the front and put on bigger tires, the headlights will be too high and you blind other drivers if you don't adjust them down a bit.
Hard to believe that 18" rims are the smallest rim you can get now. Maybe I'm just an old timer, but I still remember when 18" rims for exotic sports cars. Now they're just the base model rim. It took me a while to actually find the "smaller" rims while still getting most of the options I wanted.
Thanks for the compliments, for the most part I really like the 2015. GM did a great job on the interior upgrades. I'm still trying to like the exterior more than the last generation. But I suspect it will grow on me just like they did back in 2007.