Vested right to proceed. The applicant, or any successor to the applicant, for all or any portion of the unified development, shall have a vested right to proceed according to the plan, and no subsequent change or amendment to this Chapter 325, Zoning, Chapter 281, Subdivision and Land Development, or other governing ordinance or regulation, shall be applied to affect adversely the right of the applicant, or any successor, to commence or complete any aspect of the approved plan or materially increase the amount of site improvements or the projected cost of construction of buildings and site improvements, for a period of 20 years from the date of approval of the plan.