At any rate, we know the basic details of his story are true, as BAH confirmed that he worked there, and the government has not denied that the PRISM slides and the FISA court order are real. Given what he has shown us so far seems to stand up to scrutiny, I'd say his credibility is fine. A few random people on HN speculating about what the NSA would or wouldn't do, versus now well confirmed knowledge that he did work for the CIA, and for the NSA as a BAH contractor? I'll take the latter as having more weight.
And if he didn't have some fairly serious access, how did he get the PRISM slides and the court order in the first place?
Anyway... not saying every detail of his story is true, but all things told, I don't see how carping about his high-school education is relevant here. In fact, I don't see how talking about Snowden much at all is relevant here. The story isn't Snowden, the story is PRISM, rubber-stamping by the FISA courts, tech companies possibly in collusion with the NSA to make our nominally "private" data widely available, etc.