Glenn, you short-changed yourself by a lot when you valued your contribution at "two cents." Oral history is, as you indicate, very important. When I calculate what I might have learned from grandparents had I been interested enough or known what to ask when they were alive, it adds up to some mighty big missed opportunities. Thanks for "weighing-in" on this key point.
Personally, I think that the Barnett claim to Pocahontas descent and many other similar claims (often tied into the Bolling family) are erroneous. The fact, however, that many people believe in these claims has little to do with lying or fabrication. Although skulduggery in genealogy has been known to happen, many mistakes are made in perfectly good faith and passed from generation to generation with no intent to deceive. In the case of Pocahontas, the widespread popularity of the "Indian Princess" in the early years of our country encouraged many who were descended from people with names like Rolfe and Bolling to think that they had a connection. It was wishful thinking perhaps, but not fraud. The "Pocahontas craze" of the early 1800s beat anything Disney was able to manufacture in the 1990s.
So, while I agree that it's important to listen to grandma and tape her reminiscences, she may be more reliable about what she knows from her own lifetime than events of 350 years ago. So your final point -- take what she says and then go about seeing if it can be proved -- is the key. If her rendition of what she was told about famous ancestors falls short of the truth, it doesn't mean that she or her ancestors were engaged in lies or fabrications. Mistakes and misunderstandings are often produced with the best of motives and passed on with the best of intentions. It's happened in my family and I imagine it's happened in many others.