To provide a developer, and to its successors and assigns having an ownership interest in the real property of the developer that is the subject of the agreement (hereafter in this section referred to as the "subject property"), with a level of security over a period of time that the development plan, and the accompanying design details, for the subject property that is approved by the Town may be completed without substantial changes or impediments; and thereafter to preserve property values by protecting against individual lot owners deviating from the development plan, and the accompanying design details; caused or permitted by future amendments to the Town laws, rules, regulations, and policies governing the use, density and/or intensity of development by an agreement granting to the developer, and to its successors and assigns having an ownership interest in the subject property, qualified vested rights in the existing laws, rules, regulations, and policies governing the use, density and/or intensity of development of the subject property ("qualified vested rights") without the developer having to immediately make substantial improvements to all portions of the subject property; and