Will FileVault 2 wear out my SSD faster?
Encryption happens on-the-fly.  If the data was written to the hard drive, then passed through an encryption algorithm that then deleted the written data and re-wrote it, encrypted, that would be hella inefficient, and would largely defeat the purpose.  I think the answer to your question is no, but of course remember that if you're going from a data set that's not yet encrypted, then all of that data needs to be processed, so that initial process of reading, encrypting and re-writing data will have an effect.