DH says no, we can organise games, leave toys out etc. I (who actually go to kids parties occasionally) think it will make our life so much easier - we've got 16 children coming and all our family, GP's etc. So 30-odd adults.
The alternative to the entertainer is to arrange someone else to make the tea, take cake round etc while DH and I run the party. Btw, my family are useless and won't even help themselves to a cup of tea, so an extra pair of hands somewhere is needed! But I can't shake the feeling that hall hire (not too much money) plus entertainer is a bit extravagant for a 4 yr old.