I give A Mean Hat A$25 for trying to hubert me out of the treasure after he knew I'd gotten it (since I said something on IRC) and almost succceeding in finding the treasure on a 50/50 chance.
I had realized early on that the text was base64 encoding, but didn't know of what. So the first thing I did was use a base64 decoder and attempt to look at both possible ones as either sounds or images of some sort with no luck.
Further thought led to another place where base64 was common, which was PGP encoding, signatures and public keys. I tried importing each of them as a public key to no avail. I then went and hunted up IdiotBoys public key (finger matt@brain.mics.net yields it). I then assumed that this might be a signature to some message, so tried reading it as a signature for various pieces of text. None of these seemed to work with the first version of PGP that I tried (version 5.53), but I noted that IB's public key was generated with version 2.6.2, so I grabbed that version and tried it.
After quite a number of iterations of possible texts (and a bit of headache all around since I'm not really much of a PGP user) I finally determined that it was in fact the signature to a message consisting of the text 'This one is TRUE.'
(for the curious, the other was a signature to a message consisting of the text 'This one is FALSE.')
Had I been more familiar with PGP this might have been an easier treasure, but overall, it was quite a pain.