I actually do feel like when I've been in parking lots and moving slowly, I've heard crunching sounds a couple of times from the front like I ran over something brittle - which surprised me since I didn't notice anything big on the ground. And no, this was not hitting a curb or a wheel stop, just rolling slowly on level ground. Last night I got home and it looked like there was a big bulge or warping of that wheel cover, and on closer inspection it had not warped but rather had unseated on one side about 3/4". A firm slap on the part sticking out seated it firmly back in place. It didn't feel like it was loose enough to just fall off, but I wonder at highway speed whether a bump could make that happen.
In my 35 years of driving, it's interesting that I've never owned a car with "hubcaps" or wheel covers before, even the budget cars like my 1st gen Prius with its skinny 70R14 tires were on solid one-piece wheels. I look at those random wheel covers littered on the side of highways and off-ramps and wonder what happened....