Boundaries of a special service area may be enlarged, but only after hearing and notice as provided in Sections 27-30 and 27-35. The notice shall be served in the original area of the special service area and in any areas proposed to be added to the special service area, except when the property being added represents less than 5% of the equalized assessed valuation of the entire original area, as determined by the clerk of the county in which the land is located, the notice by mailing requirement of Section 27-30 shall be limited only to the area to be added and not to the original special service area. The property added to the area shall be subject to all taxes levied in the area after the property becomes a part of the area and shall become additional security for bonded indebtedness outstanding at the time the property is added to the area.