There's value in good 3 letter words, but as far as good random letter combinations, you're not talking all that much (low $xx - low mid $xx). Potential value is there and I think it will ultimately increase so they'll be good to hold on to but they're not bringing much in the near future. However, if you can get your hands on 3 letter words or meaningful combinations, then do so IMHO.
I have a couple .cc domains myself, the strongest of which being Attorney.cc