Sorry to open with such a green picture...but this is what we're dealing with on deck. I mean, the lines (they call them ropes on land) aren't in horrible shape and if I had tons of money I might just have them all replaced, but I don't.
I am replacing some of them - the ones that carry heavier loads like the outhaul (it pulls the mainsail out of the mast towards the back of the boat). The only bad part is that lines are expensive and if you want them to put the nice little fisheye loop in the end it takes time (it's on my list of things I need to learn how to do).
So I scrub...and scrub. I pressure wash, I soak, I try almost everything while trying not to rough up the lines too much. Some of them come out looking pretty good (see pics below). Then, just as I was starting to get the line scrubbing blues, I found a bunch of used line out next to the marina dumpster - some of it looking better than what I have now - jackpot!