Nope, you're going from one extreme to another, the bridles do not to be washed every time, no one does that. You're kidding yourself if you think that they are after every sesh.
The kite can't survive 150 sessions per year for 9 years. As you said, that's plain silly thinking. The colors fade away, particularly yellowish spectrum, and the fabric stretches. After 300 sessions this is clearly visible. The pulleys are so abraded they need to be replaced, providing you are looping the kite quite often.
Proof of the salt deposits are mostly on tips and can't be brushed away. That salt deposits create a tiny crystals and they (plus sand), eventually abrade the bladder on tips. How would one brush off from inside the LE is unknown to me.
If yours look great that means they do not 'live' in an harsh environment and punished by the kiter. Better question is, what's your riding style? I've got an 2006 XBow which hardly seen any water, looks great, with still crispy fabric.
So, the valves are off...?
Happens with the old kites you know.