I wash my bar and lines every session, salt and sand are the biggest killers of kite gear over time. I always tend to release my quick release and run water through it also, take care of you gear and it will take care of you.
My 2008 bar and lines from my old Cabrinhas and they look like near new, I learnt on, traveled and used these kites extensively.
I've taken a look at buying some second hand gear before and it's amazing how destroyed the gear is from people not looking after their lines, I now only buy new because of this fact.
P.S - My 2008 kites are FU**ed though - I've had repairs on each, one leading edge popped in Brazil and the other needed attention while in Egypt.
Thought about selling them but they are worth nothing, even though they fly sweet, will use them in the waves now.