This seems to be an inactive post, but I ran across it when I tried to research for HND lounge option.
Anyway, my leaving this message is simply to encourage anyone having a layover at HND to go landside. 4 hour is definitely sufficient, given the Japanese efficiency. I don't find any problem clearing arrival immigration. For departure, use the new "North" departure checkpoint. Most people simply went to the "Center" one intuitively after checking-in, but my experience is that there are fewer traffic at the North checkpoint. Don't even need to use VIP lane to breeze through security and passport control.
HND is really a fun airport. The international terminal itself has many shops/restaurants to explore. There are also easy and frequent shuttle buses, free of charge, bringing you to the two domestic terminals. All three terminals are equipped with observation deck. And there are many souvenir shops and JAL/ANA stores inside both domestic terminal. It's really a paradise for any AVGeek imho.