If you searched and read all the threads, you know that it can take a while to clear immigration and customs, then on your return you have to clear security and exit immigration, all of this can easily take off 1.5+ hrs. I don't think there's much you can really accomplish by going airside, as it takes about 1 hour just to get to Tokyo from NRT. Even going to Narita is not worth the rush.

Staying airside, there is a shower and day room facility that you can use.
http://www.narita-airport.jp/en/guid.../index_t2.html

Hope that helps.