Well I guess it just depends on who you cosplay as. Since Inuyasha is usually paired up with Kagome/Kikyo, that lessens possibilities.
But more importantly, is true, Mugen and Inuyasha have too much in common. Both have egos and tempers bigger than Tokyo. Only difference is that Inuyasha has a changing-to-bigger sword and Mugen has a higher dexterity, like a score of 18
. At the same time Inuyasha cares too much about issues, while Mugen plays it cool and cares very little about anything most of the time. Though Miroku and Jin would fit together, and Fuu and Kagome would fit so well that the guys wouldn't even know what they're talking about. The only violence spark would be if Miroku tried to ask Fuu his famous question.