Base on posts to this board, availability is determined when you check in.
Seating in the lounge was increased during the renovation a few years ago, and additional "overflow" seating is just outside. You should have a good chance of adding lounge access, unless there is an event drawing many VIPs.
You might want to request a suite near the lounge/lobby, since many suites are quite far away.
Signature Suites include lounge access (and show seating), and prices are scary