No decision needed. Look all you want, but the liability is on you if someone decides your computer is of interest and data is questionable. Unless you report it to vender in a verifiable way, data on the drive, even if it was not yours, is now yours in any examination. Report it in writing or no evidence will exist to point in someone else's direction for liability.
Wiping beyond technological limits of retrieval is important with both criminal liabilities and civil copyright liabilities. The odds of old data being a problem in your life may be low, but it would be icing on the cake with any situation bringing your drive to the attention of some types of investigations.
Call it paranoia if you like, but why drive around in your new used-car with a suitcase in the trunk that came with the car without knowing precisely what is inside. Remove the suitcase, or examine every square inch of it looking for contraband..