When I spray painted my grill, it held up well for 3 months. I stripped it myself to repaint it.
Its all in prep work.
The grill is also against the wind when driving, so it tends to get more damage, but my painted insert also never had many paint problems either.
Car looks great.... I'm going to repaint my grill againt o how I had it before.
should end up looking killer again.
Alon