Thanks guys. Sun damage and general wear from the downrigger has to take its toll, but to what extent? I hear Spectra is fairly UV resistant. I assume most are using original PowerPro spectra or Scotty's spectra.
If I had to guess as to when to change for a typical rec boat, it would be 3 years on most riggers, and double that with a Scotty electric or a rigger that gets covered up each day, as long as the last few feet are trimmed 2x a year. I would also expect heavier weights will affect its life as will 250lb vs 150lb. Of course coming into contact with something underwater (like debris, or a wire line) could drastically shorten it's life!
It seems expensive compared to wire if it needs changing every 1-2 years unless you're a busy charter.