I've been disappointed with the Ambassador program. From my understanding, it was supposed to be about more personalization; but I'm not seeing much difference than SPG Platinum. In fact, often things done via my Ambassador are less effective and beneficial than contacting the property myself before arrival.
LOL, I'm still having trouble getting basic Platinum benefits like small fruit baskets in my room, ROTFL.
IMHO, the Ambassador program is little different than the SPG Platinum concierge, as the original poster asked. I don't seen much benefit; except for perhaps a chance for a better room upgrade over other SPG Platinum members; and since I prefer to book online myself (takes less time than contacting a person), having someone to do bookings for me is not useful.