First the sensors:
Contact with the rotor wears off the head of the sensor and as you said
a ground signal then sets off the light.

The sensors are cheap and considered disposable and should
be replaced when pads are replaced if they have set off the light.

I don't replace mine or use them anymore, I am pretty good at
knowing how long the brakes will last.

As for the caliper, if it works properly you probably do not need to
worry about rebuilding it. Yes, dust boots do deteriorate but should be okay.

What part of the country are you in ? Maybe your weather conditions
would be a cause for concern.

Others here will have better input on the caliper.

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80 300D 340K Owned 30 yrs
83 300SD 440K Owned 9 yrs - Daily Driver 150mi/day
02 Z71 Suburban 117,000
15 Toyota Prius 2600 miles
00 Harley Sportster 24k
09 Yamaha R6
03 Ninja 250