I was there last year (and will be again this year). From what I recall, your Bay Grandstand Ticket includes Zone 4 and Zone 3 Walkabout access and there are at least 2 viewing platforms in Zone 4. I don’t remember any checks as these are in the “public” areas. If you come in via Gate 3 (City Hall) and walk straight ahead towards the Bay stand, they are stiuated on your right. Just for info, there are checks on paid grandstand access over and above access to the circuit.
For what it’s worth, the view across the Bay from the grandstand is pretty amazing with laser and light displays on the commercial buildings and the waterfront