I prefer the UA IFC to the ANA IFC lounge, but they are both nice and it's really a matter of personal preference. Together with SFO, the NRT F lounge is the nicest in the system.

Also, UA F will get you through the F security entrance, which is always very quick. Immigration is rarely longer than 5 minutes going into the airport.... but could be a bit longer getting out of the airport.

I would recommend a trip into Tokyo. Take the Narita Express to Tokyo station. You could wander around Ginza and/or the Imperial Palace. Also get a nice lunch. It's a very easy trip. You would easily have 5 or 6 hours in Tokyo. Well worth doing if you've not been to Tokyo before.

Also there is spa in Terminal 1 (*A) on the 2nd floor between the North and South wing. Clean but not too fancy.