I know -- I refuse to fall off the Snape bandwagon.

if Snape is going to spy internally and even if he gathers Tommy's most secret plans, who in the Order will believe him?

I agree that's a problem -- Snape is so far in with the DE's that no one in the Order will believe him now. However, I still think that he will be able to counter Voldemort's plans, and possibly provide Harry with unexpected assistance in the final showdown.

And, if Harry should fail, then Snape may be the only hope Dumbledore had left to defeat Voldemort. And Dumbledore could not let Harry know that, since Voldemort can still read Harry's mind.

I know, I know, I'm really in denial, aren't I?