You’ve been to NRT a few times already, so you must have a general idea of what there is there.
Narita Airport has an excellent web site which catalogues all the shops and attractions in both the terminals – both landside and airside.

Whether it is ‘worth it’ or not it is entirely up to you. If you were to stroll as quickly as you can to Customs and immigration and see what the queues are like for that day at that particular time you can decide for yourself if it’s worth the hassle. To be absolutely safe, plan on one hour to leave the airport and another hour to get back in, this will leave you with 5 hours.

Then, my advice is to forget the airport, get to the Keisei train terminal, buy a 250yen ticket to Narita Town (no more than 15 minutes). Mooch around Narita for 4 hours or so and return on a train that will get you to the airport AT LEAST an hour before your flight departs. There’s an awful lot you can do in Narita for four hours, restaurants, cafes, bars, shops with traditional items, a major temple, even some public baths (take a towel).