I've got a feeling that if enough people encrypted all of their data the NSA would just hire more cryptologists.
That's just it, they can't decrypt it. At least not yet. That's why they are storing it all, so they can decrypt it later when (if) technology allows for it. The public adopting mass encryption would be like a DDoS against the NSA. At some point it becomes impractical to just build more datacenters, buy more computers, etc. They would have to be much more selective in which individuals they spied on, like they should be doing already.
And yes, they would need a technological breakthrough like Quantum Computers to even have a chance to break modern cyphers. Brute forcing a randomly generated key would take longer than the universe has existed. If encryption didn't work, online banking wouldn't be safe and bitcoin would be dead right now.
Take AES for example; AES is one of the most common cyphers, is used by the NSA itself, and modern CPUs even have specialized hardware decryption support for it. It's been around for 12+ years and is still the first choice for symmetric encryption. A 256 bit AES key has 1.1e77 possible combinations-- that is only a few orders of magnitude less than there are atoms in the observable universe. Even futuristic computers won't guarantee decryption because you start running into laws of physics.
The NSA hoards all this encrypted data in the hope that one day a weakness will be discovered in the cyphers that reduce the searchable keyspace down to realistic levels. (unlikely) Or in the case of symmetric encryption (i.e. disk encryption) that the user created a weak key. Or they hope to get the key via some other means, like a keylogger or a man-in-the-middle attack. At the very least encryption prevents casual snooping as it would require them to commit considerable resources to decrypt your data. No more 'lol check this phone call out dude!'
It's easy to encrypt your data nowadays btw. Truecrypt is free, polished, easy to use, fast, and effective. I encrypt my media drives, and the performance hit is entirely unnoticeable. My VPN provider created a pretty braindead easy client too. And enabling SSL for usenet is clicking a checkbox. It's not like I'm going out of my way to do this.