A project area need not be restricted to buildings, improvements, or lands which are detrimental or inimical to the public health, safety, or welfare, but may consist of an area in which such conditions predominate and injuriously affect the entire area. A project area may include lands, buildings, or improvements which are not detrimental to the public health, safety or welfare, but whose inclusion is found necessary for the effective redevelopment of the area of which they are a part. Each such area included under this section shall be necessary for effective redevelopment and shall not be included for the purpose of obtaining the allocation of tax increment revenue from such area pursuant to Section 33670 without other substantial justification for its inclusion.