Two times I have used a ambassador so far;

1) To try and get SPG to honor the $20 Four Point/Coke promo. They worked their magic, but it took some time - and the platinum desk may have resolved it anyways.

2) I basically called them and said I have a beach vacation in Florida in mind, what are the rate options (points, points + cash, etc) for various rooms in different properties. They e-mailed me back a list of 7 or 8 hotels with the room types, etc. I thought that was pretty cool, they basically did a lot of the homework for me. Some room types I can't even see online, etc - so I would have called them anyways. But for them to do the homework - that saved me a few minutes of time.

Is SPG ambassador worth it? Tough. I wish the Ambassador acted more like Santa, like if I am asking for a SNA in a great property, or obviously on vacation - surprises, treats, and other signs of recognition are appreciated. A small vase of flowers, some wine and snacks/fruit, or even a personal note suggesting my ambassadors top suggestions for me at the hotel XYZ.

This is free service, and I do get a occasional fruit or wine offering. But I think you get what I mean by trying to offer a little something more....