Unless approved by the affirmative vote of three-fifths of the electors voting thereon at a regular or special election, the City of Southgate shall not sell, exchange, lease or in any way dispose of any property, easements, equipment, privileges or assets belonging to and appertaining to any Municipally owned public utility which is needed to continue operating such utility. All contracts, negotiations, licenses, grants, leases or other forms of transfer in violation of this section shall be void and of no effect as against the City of Southgate. The restrictions of this section shall not apply to the sale or exchange of any articles of machinery or equipment of any City owned public utility which are worn out or useless or which have been or could, with advantage to the service, be replaced by new and improved machinery or equipment, to the leasing of property not necessary for the operation of the utility or to the exchange of property or easements for other needed property or easements. It is provided, however, that the provisions of this section shall not extend to vacation or abandonment of streets, as provided by statute.