I wouldn't worry about the electronics in the KX. They've lasted this long with no problems so should carry on for a while yet, and they're of the age when you could spot individual components on the PCBs so it should be possible to rebuild the electronics if they fail.

IIRC the K2 and KX had a better light meter than the KM/K1000. Certainly my KM and K1000 have very interesting ideas of accuracy while the KX and K2 are dead on.

Pretty sure I've seen mention of Spotties with MLU as well. The article suggested that it was a factory option and that if you ordered it you ended up with another switch on the lens mount, like the meter switch but on the other side.