Pennsylvania's largest health insurer has spent $32 million in the past eight months quietly acquiring vacant land and commercial property throughout Western Pennsylvania as it pieces together a new $1 billion health care system. Highmark Inc., using shell companies, has bought property in five municipalities, stretching from Cranberry in Butler County to South Strabane in Washington County, as it seeks to compete with rival UPMC and draw patients to a struggling hospital network the health insurer wants to buy. Highmark officials declined to comment on specific plans, but it's likely the insurer will build outpatient medical centers on the properties, raising questions about duplicating medical services that increase the cost of healthcare.