I redid my grill block recently. Went a bit more aggressive and used some peelable caulk so I can take it off at any time.
I also pulled the OnStar fuse. It's a 10A fuse in the box by the driver's left knee. That's pretty big! 10A*12V means that OnStar is potentially pulling 120Watts, which is maybe even more than the headlights.
Can't say I noticed any difference after pulling the fuse, plus now there's no possibility of being tracked via GPS.