I'm here right now having recently dropped to gold. I had booked a "premium floor city view" room and my upgrade was to a "premium floor bay view" room -- essentially moving across the hall. No lounge access for me.

Breakfast access in the restaurant is via a list of names and statuses, with separate laminated cards for gold and diamond at the restaurant. As gold it's the continental breakfast and upcharge for full breakfast is $6 although this has been waived 2 of the 3 days I've eaten there. I overheard a diamond next to me in the restaurant being told that the entire breakfast including hot items was free. So it appears diamonds have a choice of the lounge or restaurant. I would highly recommend the restaurant versus the lounge (which I've been in before, just not this trip) for the variety of items. Hot items in the restaurant include made-to-order omelettes ordered from the server, and scrambled eggs, potatoes, bacon, sausage, and some Chinese items on the hot side.

I'll update the breakfast wiki with this information.