This is what the
DVC member's site said about valet parking:
"As of July 16, 2001, the Walt Disney World® Resort will adopt a standard industry practice and charge for valet parking at all Walt Disney World Resort locations that offer this guest service. The $6.00 fee (among the lowest in the market) is a daily charge, so once you have paid for valet service, you will receive unlimited valet parking for the remainder of the day.
However, Disney Vacation Club Members will not be charged for valet parking at Disney's BoardWalk Resort and Disney's Wilderness Lodge, regardless of where they are staying. Disney Vacation Club Members must show their DVC Member card or Walt Disney World Resort ID indicating that they are a "DVC Member" when leaving their vehicle to be parked in order to receive this service at no charge at either Disney's BoardWalk Resort or Disney's Wilderness Lodge. Members will be charged for this service at any other valet parking operation at the Walt Disney World Resort. Whether or not you are charged to valet park, gratuities are still appropriate. There will be no charge for guests with disabilities with the proper permits. This charge only affects guests and Members who chose to use this service. "
Here is link to another thread that implies guests of members are charged:
http://64.225.125.24/forums/showthread.php?s=&threadid=73103&highlight=valet
But the info from the Members' site does sound like if your resort ID says "DVC Member", you are not charged for valet parking.
Since you are staying with your guests ( and everyone in your party should get a resort ID that says "DVC Member" on it), I'd suggest you call MS next week and ask them.