The vast majority of "conspiracies" are more like Underpants Gnomes business models. There's no explantory proposition anywhere. There's no overwhelming theory - put ten truthers in a room and you'll get ten wildly different theories (if you get a theory at all), and no overwhelming facts.
Watergate didn't require any theory - people connected with the Nixon administration were caught red-handed breaking and entering. It's obvious why they might do what they did and to ask who knew what/when. It was obvious people had a motive for covering up a criminal action. It was just a matter of documenting it.
When Iran leaked the Iran-hostage story via a Lebanese newspaper, nobody had a conspiracy theory before that. There was no "why would Reagan do that?" - the motivation was obvious and it was in print. When the -Contra side came out, no one had a conspiracy theory about a connection there. It was more investigation/leaks and a total surprise.
So I don't see where Conspiracy Theories really equate to uncovering Criminal Conspiracies. They seem to be more exclusive than related to each other.
Thus, Iran-Contra is not a conspiracy theory because it's true, even though it is a conspiracy.
If you asked a average person three years ago whether they thought that all their calls were being recorded and that the NSA was hacking into companies and stealing data you would have been called delusional and your explanation would have been bizarre and unreal. Yet here we are today with clear evidence that all these things are being done with no repercussions for the perpetrators.
A person can still be operating under a conspiracy theory and talk about pervasive government surveillance. Just because it's true doesn't make it not a conspiracy theory.
But also, for your example, anyone paying attention had been saying, pretty loudly, that governments were surveiling their populations. See, for example, the EU parliament report into ECHELON. We know about ECHELON in the early 1990s. Thus, if someone had said "They've done it before, look at ECHELON, they're probably doing it now" -- that's a reasonable bit of evidence and a reasonable conclusion. If someone says "I hear clicks on my phone line and so the government is spying on me" that's a conspiracy theory (because the evidence is bogus) even though it's true (governments do spy on citizens).
It's also a typical trait of conspiracy theories (in the negative sense) that they pretend to have figured out more than they possibly could have.
I mean they don't just sell you suspicions (that might even be reasonable), but overdetailed debunkings which are clearly fabricated.
As if they believed that the winner is whoever provides more details, wherever these would come from.