Mystery is not just absence of info. Which is all there is. You need some info (namely that he was great and and hard to beat with great knowledge of the Force) but not about his exact intentions.
Hitchcock rule for suspense: the audience knows more than the heroes do, that will enhance your sympathy and empathy for the heroes. This is where the PT fails so far.
Again, yerss, I can't help thinking you are stating the obvious here. That said, it doesn;t matter if Sifo-Dyas was dead or not, did it? Why would it help to impersonate a dead Jedi? What difference would there have been if he had impersonated a live one?
And still there is the name similarity, and the shifty looks which clearly show there is more to this.
Hmm
I registered just for this topic. I already posted this reply, but it didn't work so I'm posting it again.
I'm not an avid Star Wars fan - I've seen all the movies, but I'm not that great at trivia and things like that. From what I got from the movie, however, was that Sifo-Dyas is actually Dooku. He's a very powerful Jedi, and Yoda seemed to know him. In fact, during the Yoda/Dooku fight scene, Dooku comments on how he was once Yoda's Padwan-Learner (I know I butchered that spelling, sorry!). So from that, and the shifty looks given by Windu and Yoda, I just gathered that Sifo-Dyas faked his own death, moved to Geonosis (spelling, again), and became Dooku.
Also, it was obvious that Dooku was in cahoots with Sidious, and if the Sidious=Palpatine theory is correct (which we all pretty much think it is), then he could have went along with it fine. Also, all of the clones were based off of Jango, and they seem to know each other also (despite what Dooku might say - Jango defends him during the battle).
Just my two cents.