From my own experiences at this hotel, and that I live about 200m from it now:
1 - Always free lounge access as Marriott Gold, this includes breakfast and free cocktails/nibbles/champagne in the evenings at this hotel. No different than any other Marriott hotel that isn't a resort.
2 - AFAIK Free breakfast in the main restaurant is only offered when the lounge is too busy to accommodate you (bearing in mind the lounge has an egg chef and is going to be far superior to anything you know from the US, though perhaps more restricted than some other Asian Marriotts). This policy differs from many in China.

Otherwise, in theory you get a room upgrade but it is unlikely at the hotel, and even then the rooms are very small, particularly by American standards.

As such, save your HK$800 for something else in Hong Kong, plenty of chances to spend that cash - your HK$800 probably doesn't include breakfast in the main restaurant anyway, but you would only just about pay that much for breakfast in cash if you really wanted a wider selection