Yes, you will get full platinum benefits inc the club lounge on the 21st floor.
This is an excellent property, I stay there regularly, in fact checked out this morning. IMHO, better than Sofitel and given the platinum perks such as the excellent club lounge and upgrades provides great value for platinums.
The lounge service is abundant both morning and evening in respect of both food and drinks. In the morning, you can also elect to use the restaraunt instead of the lounge for breakfast which has a great spread much bigger than the lounge and maybe a bit better in that sense but not so private. You can also use both; have your main breakfast in the restaraunt and then head to the lounge for a coffee, relax and read the paper.
I really do give this property 10/10 it's great. Be sure to use the gym and pool on the roof!
(Excuse iPhone related typos!)
SSNZ