One of the biggest issues you must confront when sanding plastic is heat...sanding friction causes heat, and plastic parts absorb the heat. Metal parts also warm up from the sanding friction, but metal tends to reflect the heat back out again. Because plastic parts absorb heat, they can soften or even re-flow under power sanding.
Sanding plastic is a good thing--it effectively doubles the surface area, providing twice the opportunity for a new coating to adhere to the surface. Even a light scuff-sanding will help with adhesion...there are just more places for the new coating to cling to.
On the other hand, too much sanding can cause problems--like the "hairing" that you'll see when some plastics split and melt into hair-like strands. Too much power sanding can also cause thermoplastics to reflow. After a forceful sanding, the scratches are very evident. But walk away and when you return just minutes later, the scratches have disappeared--the heat melts them flat again.
The moral of the story is: always be careful on plastic parts. Turn the air pressure way down or even sand by hand to avoid heat buildup!
For more information on sanding plastics, check out our website at www.abrasiveresource.com
