I've taken the front bumper skirt off the cappuccino to repaint it. The scrape on the corner has sanded off with 800 grit but the rest of it is peppered with stone chips. Do I sand the whole thing back until flat or do I spray it with a spray filler and flat that back. I think the filler would be less work but will it be less good?

just done a similar repair on my mums BMW, i just used high build primer and flatted it back (3 coats), looks just like the factory finish, save yourself the hastle of rubbing ita all back

unless you are using aerosol cans which for some reason cant apply the high build primer very well, at which point rub back with fine wet&dry and plenty of water, use normal primer etc,etc.

If you sand sown to the base plastic, you may want to give it a light spray with adhesion Promoter (loose translation from spanish) this will help a lot to keep primer and or paint attached to the plastic in the event of future scratches or small bumps. Say it will be harder to have cracks to show throug the paint.
Beware, here in mexico is an expensive product. Donīt knowo over there.....
(Well I have already posted somewhere else, everything is PRICIER HERE!!!)