This is a difficult one to answer. I have a several different ccTLD's in my portfolio... including .bz (2 letter, and 1 words). I like to have a diverse portfolio because you just never know who's going to come knocking.
Whether or not it's worth it... it's hard to say. Will you at least get your investment back?... probably. Will a 2 letter .bz be the "BIG ONE", probably not - I'm willing to take those risks from a business standpoint. It's really is a personal choice. There are many different opinions on the matter, so it will be tough to gauge the actual "worth" from a community standpoint.
When dealing with ccTLD's I generally only register names that have very high Overture or Wordtracker numbers. If I come across a 2 letter .bz that doesn't have much going for it... I'd pass, as with any other ccTLD. It has to be extraordinary. That is the key.
Just an opinion~
Jennifer