Earlier i used simple waxpol vinyl polish or any other polish to dress the plastic parts of the engine.
Now what i use is Zorrick 88. Wash the engine, let it dry completely, spray zorrick all over. Be careful that the engine is not hot while you spray, Wipe it off. It will leave good shine behind.
MOST IMPORTANTLY, PLEASE DO NOT START THE CAR JUST AFTER YOU HAVE COMPLETED SPRAYING, LET IT DRY FOR ATLEAST 15-20 MINS THEN ONLY START.
One more benefit of zorrick is that rats don't come in your engine bay, once it is sprayed. And zorrick doesn't also attracts dust.