Elsewhere (don't ask!) I've seen suggestions that tired lines can be revived by spraying with silicone.
A good idea, perhaps? It would keep them slippery for a little longer, if they're beginning to bind. But it won't repair them if they're frayed.
But how do you spray them?
On their winders? Wouldn't that be a bit hit & miss, with a spray that dries out almost immediately?
Or do you stretch them out over 25 metres, run up and down spraying one side of each, then turn them over and spray the other sides? Silicone spray cans aren't exactly cheap, so it would probably be cheaper in the long run to buy new lines.
Come to think of it, how many flying hours should one expect to get from a set of (say) Protec lines? Without spraying, I mean.