I have a KB-5181 that is very nice. Those Monterey blues are good switches and I like the lightness of the feel and sound.
My underlying question is the rate of "use" vs "wear" vs "damage" - that is, shiny keys obviously indicate a significant amount of use, but I have gotten some old keyboards that still felt great, and newer ones that were not so great.
The mushroom shape of the key caps and the vertical sidewalls of the barrels obviously keep the majority of dust and grit out of the inner parts, but am I right to imagine that the inner dirt is the real culprit that makes some boards feel more harsh?
This is the reason that I always like to thoroughly clean the parts, but not worry so much about lubricating them.
Tangentially, is there any way to tell about the condition of a spring by looking at it? If it is not bent, stretched, or rusty, what else is there to look for?
Lastly, a really good cleaning might improve those keys a bit, some of the shiny appearance might be oils or lotion.