All excellent points that I probably cannot adequately address, but I'll certainly try.

With regard to audience, I agree that it's hard to nail down exactly who Last Week Tonight's target audience really is. I think that's partially due to the fact that he's on a paid-access network, and because of that he can risk alienating some of the "unplugged-in Americans." He's not as tied to ratings on HBO, so he's insulated from having to do the targeted audience pandering you see on regular/extended access TV. The weekly rather than nightly format also may be helping with this; doing a single show once a week is far less of a commitment to ask from an audience than a nightly one.

Given how much they're trying to reach out via social media through use of Twitter, Facebook, and posting whole episodes on YouTube, it seems like the end goal here, rather than getting people to tune in every Sunday night, is to get people talking about it online wherever they can. They are trying to reach the unplugged-in Americans, but not directly; they seem to be hoping that by making everything they do available online, it will get the more sociopolitically-active types to share with their less active friends; not even that they'll necessarily get people watching entire episodes, but they'll be able to say "There's this great interview segment you should check out," and then link to thirty seconds of the complete interview. If that's the end goal, then they have to strike a balance between making the show appeal to their direct audience (the sociopolitically active ones) while not making things too esoteric or incomprehensible for those they hope to reach indirectly. It's a fine line to tread, but so far they seem to be doing it fairly successfully; I think it can be argued that LWT certainly impacted the national dialogue on Net Neutrality.

The end result, as you stated, is that many of us are left wanting more. I do agree that he could have gone a lot more in depth, and that many of Snowden's answers were cut down to the point of giving us no new information; there certainly seemed to be several points in the interview segment where Snowden seemed like he was going to elocute further but was interrupted by a jump cut. However, I don't think the goal was to present any new information, but to restate what those of us who have been following the story already know in a way that those of us unaware of who Snowden is can understand, so we have something to point to when they ask, "Yes, but why is this a big deal to me?"