Other significant design features, such as material or quality of architectural design, roof structures, chimneys, exposed mechanical equipment and service and storage enclosures, signs, landscaping, retaining walls, fences and lighting posts and standards, provided that a finding of inappropriateness shall state not only that such inappropriateness exists but, further, that it is of such a nature as to be expected to provoke, by a preponderance of the evidence, one or more of the harmful effects set forth herein and that the finding is not based on personal preference as to taste or architectural style.