Salting makes no sense on symetrically encrypted data, which is what you've got with AES-256. If anything, it'd just make any potential cracker's job easier by putting some known plaintext within the data. After all, ANY key will "decrypt" the data, but only one key will produce the original data. By putting a chunk of known plaintext in there, you've made it far easier to determine if the key being used is valid or not ("is salt text there, if so key is valid").
If the data's so sensitive that you have to take these precautions, I'd be more worried about the exposure window when the key file is actually stored on the server, as well as the traces it will leave behind in memory and on-disk, even after you've removed the file.