Expansion. A nonconforming use shall not be enlarged or extended beyond the area of the existing structure in which the use is located, which structure existed prior to adoption of this zoning law, unless granted a special use permit and site plan review approval by the Planning Board. In addition to dimensional criteria, expansion of a nonconforming use shall be considered as intending to occur whenever it is proposed that the magnitude or intensity of the preexisting nonconforming use is to be increased in volume or activity by hours of operation, amounts of employees, deliveries, amounts of customers, additional parking requirements and similar material changes in circumstances which magnify the volume of the nonconforming use.