I've seen absolutely no proof of a (properly made) FF string causing any extra wear on a properly made bow. I've been using FF type strings on my longbow for the last 15 years or so--never had a dacron string on it. Rod Jenkins puts more shots through a bow in a year than most will in a lifetime, and he hasn't had any problems.
Usually if you switch to dacron from FF, especially on a longbow, you'll notice increased handshock. You'll also notice a lot more stretch/creep in the string, and decreased durability compared to most FF materials (I can think of a few exceptions).
Chad