The benefits you get seem to vary from time to time.
When we stayed 2 years ago we got:
- Dedicated check-in
- Free tea and coffee facilities
- Free towel hire
- Room on a higher floor (we also paid extra for a lakeside view)
I think those benefits are always available.
Then in addition we had:
- Hot breakfast in separate restaurant
- Afternoon tea/snacks (we also loaded up with cans of coke and sprite there too!)
Those two were a welcome surprise to us, and they were well worth the extra money in my opinion. Without those two extras, the Admiral's Rooms are not worth paying extra for (we only paid extra to get a high lakeside room to see the fireworks, but ended up watching them in the park every night anyway, so that was a waste!).
Trouble is, you never know in advance if you are going to get any nice 'extras' with the Admiral's rooms.
We really loved the NPB - can't understand why people seem to have a downer on it. Only negative for us, was the slightly long walk.