The Bulls enjoyed a superb season to clinch automatic promotion, but manager Graham Turner is already looking ahead to the challenge of football in a higher division.
Benjamin scored 11 goals in 43 appearances for United, with his season badly interrupted by an eye problem.
Defender John McCombe has been released after just one campaign with the Bulls, while goalkeepers Ryan Esson and Michael Ingham have also departed, with the latter having agreed a deal with York City for next season.
Also on their way out of Edgar Street are youngsters Jordan Fitzpatrick and Marcus Palmer.