The 6 foot rule only applies to dwelling units and guest rooms in motels. Article 250-50(b) requires receptacles whenever flexible cords with attachment plugs are used, with no minimum number or distance requirements stated. The 6 foot rule is generally used in other occupancies for convienience but is not required. One receptacle will work if you have a long enough cord on a vacuum cleaner! That is assuming that a vacuum is used! I don't think 9 outlets is overdoing it in that size of room. A meeting room may have several loads requiring outlets, ie coffee pots, TVs, projectors, etc. Better to have too many outlets than not enough.
BTW, we have a large Amish community in our area and they don't use electricity. No electricity, no NEC.