Unless approved by the affirmative vote of two thirds (2/3) of the registered electors at a regular or special election, the City shall not sell, exchange, lease or in any way dispose of any property, easements, equipment, privilege, or asset 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.  The restrictions of this section shall not apply to the sale or exchange of any articles of machinery or equipment of any City owned 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, or to the exchange of property or easements for other property or easements.  The provisions of this section shall not extend to the vacation or abandonment of streets, as provided by law.