The minimum number of parking spaces required for a use not specifically enumerated under this section shall be the same as required for a use of a similar nature as determined by the appropriate board based upon that use enumerated herein which is more similar to the proposed use. If there is no use enumerated herein having sufficient similarity to the proposed use to enable the appropriate board to establish rational parking requirements, the appropriate board may, in its discretion, direct the applicant to furnish the appropriate board with such date as may be necessary to enable the appropriate board to establish rational parking requirements. If two or more combined uses are identified, the minimum number of off-street parking spaces required shall be for the use requiring the most off-street parking spaces.