From the concerts I've been too at Makuhari Messe, I find other than some after parties, there isn't much of a concert goer atmosphere in the surrounding area. But at the same time korean pop concerts tend to attract a different crowd than I'm used too so it may be different. I will say though, if you stay near Makuhari Messe, you are going to be all in for the concert experience because there really isn't much out there other than the convention center, a mega shopping mall and a baseball stadium.