Car counters in parking garages work because the entrances and exits are designed so that there is no physical way for two cars to enter or exit simultaneously (next to each other in parallel). If you cannot assure this for the room people are in, then all couning methods will be inaccurate. How inaccurate depends on the number and widths of the doorways. Also, bi-directional is bad in this application. The ultimate would be one guzinta door and one guzoutta door, but that probably is not practical. Direction can be determined with two sensors per doorway and some logic, especially if the physical arrangement assures that an exiting person will clear both sensors before an entering person overlaps one of them.
As above, we need more information about the venue.
ak