If they have identified you as a target, and they really want to get you, have time and the resources - probably not much, e.g. they could break into your house, and install a hardware keylogger in your machine - a VPN wouldn't help much!

But isn't their method of operation: Collect Everything and see if we've got something on someone later if they're going 'rogue'? (E.g. against the establishment)

Yes, but that would be worthless without the next step of targeting an individual identified by the dragnet. I imagine all you need to be a person of interest is to have communicated with someone who is a small number of hops away from some other person of interest. Or later, when they really get going on their data mining, all you'll need to have done is to have said something particularly interesting and negative about the NSA or the government; they'll have to start doing that, because they'll run out of actual terrorists and they'll have to find a way to keep racking up "successes."