The couples massage is good idea, since no doubt it is something they wouldnt do for themselves. Mentioning a special thank you and Congrats/toast for their anniversary also is a great idea. Being in those shoes (I am the MOG, helping out), parents don't like to see their kids spend a lot of money on them, especially when there's wedding costs right now. Showing and knowing your are being appreicated is really a big thing in it's self. If there's time, maybe even before you leave, have mother/daughter lunch and go get a pedicure, have a special day, just the two of you!