One strong point for the bootstrap paradox: Brynden had to be trying to teach Bran something by going to the past at that critical moment. I mean, the cave was under attack and they both were strolling through the past.I can think of two kind of lessons to be taught, one practical and other more philosophical. The practical is more obvious: "Look, Bran, you can change the past". What's the problema with this kind of lesson? Well, like Brynden said, "the past is already written, the ink is already dry". I think that's the problem with the bootstrap paradox: even if you can go back in time, you won't be able to change anything - in the best (or worst) case, your attempt to change the past will be the cause of the event that you were trying to change in the first place. And that's a strong point against the bootstrap theory: The power to change the past is useless.
Now there's another thing that Brynden could be trying to teach Bran by showing him Hodor's past. What if Brynden foresaw the cave attack years before current events? What if he decided that Hodor would very important to Bran's mission and tried to show this to Wyllis (and thing went really bad, like we saw)? I know, this is a very long shot, but by showing Hodor's past, Brynden could be trying to explain how important Bran's mission is, and that sacrifices would be needed to fulfill that mission.