I stayed in the hotel in december and got a small suite with a view of the castle (Lomond suite I think it was).
Didn't ask for an upgrade, it was all ready and waiting. Platinum amenity is a full bottle of red wine.
Lounge access should be available to you as well. It's only open for an hour in the morning, couple of hours at night. It's basically two rooms knocked together with a TV, nibbles, drinks, newspapers. Staff were great.
Don't forget to try out the 'one' spa as well. Can't beat an early morning soak in the hydropool....it's outside on the roof, very strange in the middle of a scottish winter!
If you've got any specific questions let me know.