I believe the white gel coat is nothing more than primer and yes, sand the snot out of it! You can get a real nice surface (all the waves disappeared) and remove quite a bit of weight. I don't remember the exact numbers but it was measurable and significant.

Additional primer may then be required for the seams and any defects.

Edit - Just to be clear, I'm not talking about a light scuff. Start with dulled 150 (albeit briefly!) with the intent of removing the primer. If the surface is opaque white, then there is too much material and sand some more.