Oh, its not that I think Tobi=Tsunade's dad (the though with the mask and respirator we could have a star wars moment!).
I think there is some key connection that perhaps could be made between blood lines as well. I guess I look at someone like Minato and look at the physical traits he has similar to Tusnade, and then the similar personality traits of Nawaki and Naruto and wonder if perhaps there is some relationship or key that connects this group of people together a bit better.
Looking at blood-lines to see if we can find something relatively important here, and the potential for Naruto as well as perhaps an indicator of what he could possibly do.
We always use Kushina as a way to draw out the fact that naruto is in fact connected to a direct link to the Senju clan and more importantly the younger son of the SoSP. Minato has to have more importance than he is being show, and I believe there is a purpose in the amount of ambiguity that is being given to us.
Eventually, I'd like to draw the conclusion that Naruto has a more direct relationship to Sasuke. He is "the child of prophecy" meaning I have an odd feeling that something will occur to trigger his latent ocular jutsu, completing the picture.