Is there something which I can do as someone accepting meaningful untestable beliefs that I can't do as a positivist? Certainly there is some meaning to the sentence:

On August 1st 2008 at midnight Greenwich time, a one-foot sphere of chocolate cake spontaneously formed in the center of the Sun; and then, in the natural course of events, this Boltzmann Cake almost instantly dissolved.

but the positivist might simply say that you can give this a meaning, but science does not need to to do its job. I'm not saying that there isn't an advantage to talking about the meanings of sentences without experimental results, i'm just saying that to refute positivism you have to show that science does something you cant do by simply defining beliefs in terms of predictions. You have to give an example of science doing something successfully which commits it to the meaning of an untestable belief.