Hey Kyuubi,
I'm on right now ;-) I'm definitely reading the manga again. I was busy with studies and my hobbies for a while but I have a lot more free time in the moment.
I don't know what I think about this right now. But I'm on to the heritage-theme myself since the essence of yin yang chakra is simple enough. If you don't get it then read yasha's thread on it, I think he's got it right.
As for the heritage, I think that there are the direct descendants of Rikudo which are Senju and Uchiha but there are also the Uzumaki which are relatives of Senju and obviously blood-related to Rikudo as you can see on this chart.
http://www.narutobase.net/manga/Naruto/462/13 These clans carry all the abilities that are interesting for Naruto and Sasuke. "Modern Ninjutsu" carries normal chakra which is already yin-yang mixed. This kind of chakra is only able to mimic elements. Then there is philosophy. It's possible that the monks carry special abilities:
http://www.narutobase.net/manga/Naruto/314/7 I don't think this should be ignored completely.
Karin's an Uzumaki, Naruto might find this out soon enough. What do you want to bet that Haku was an Uzumaki?