One caveat to the handover consensus: if insulation or concealed drainage work is the main concern, some elements may already be covered by then. A pre-completion inspection could be worthwhile only if access is permitted at the relevant construction stage. Otherwise I’d spend the single visit...
My first reading would be property-level variation, especially for detached homes where condition and exact location can create huge differences. Thirty days alone is not enough to establish a change. Recent completed sales would be more persuasive: did renovated homes actually sell near asking...