Right, those are the two commonly used arguments in favor of Fibs. I go by the evidence from actual market data though.
LOL, there is a thread on FF you would like. There's a guy who claims that the market is completely predictable using Fibs, if you only pull them in the right way. He gives hints out every so often, and all these people are on there trying out a million things to make it work.
It's kind of funny because the thread has thousands of posts of charts with these lines all over the place, and after all of this there is still no clear set of rules for how to do it that anyone can test objectively.
Every once in a while someone will get frustrated and question whether they're all on a wild goose chase, but then someone comes up with a new idea and they all go nuts trying to find the holy grail again. Except they call it the "moley quail" on that thread because apparently the term "holy grail" is looked down upon there.
A lot of them are pretty sharp though, and they have a lot of fun in their quest. Who knows? Maybe they WILL find the "moley quail" using Fibs.