By the way, I was liking all the mechanical switch talk. When I started reading this thread I was sure dibi just filled it with magic dust and monkey poo. It turns out that's what a spring is...
What if you had a wedge shaped piece of copper, stainless whatever connected to the bottom of the button that, when pressed, wedges between two contact leaves... The leaves would have some flexibility allowing the metal to rub a little bit each time the button is pressed. This would keep the contact clean.
This is sounding similar to what Mundy is shooting for with his fingerstock parts, but a cylinder into fingerstock instead of a wedge into a \ / type contact.