The general rule for 12' spacing applies to Residential, not Commercial occupancies.
An event hall is a heavy user of electricity, as well as water and other utilities. The spacing requirement may just be to get a price based on an estimated receptacle count. The finished drawings should show where they should all be located.
Also, in such an application it is not uncommon to require a separate circuit for each receptacle...make sure that you confirm how many panelboards and homeruns you will need before you commit to a number.
Good luck with your Bid.
