I agree with your engineer (but then, I am one too). A 1Meg is a much smarter choice than a 100 since it will cut down on chassis currents rather significantly. I am assuming your amp has chassis ground.
The small cap would be there to filter out noise from the power rail. Your amp probably already has a few of them here and there so one more can't hurt.
You definately don't need a high power rating. 3W would be way overkill - 0.5W is plenty. However for the cap, make sure its voltage rating is twice your rail voltage.