It's serious, but there's the possibility that Plasti-Dip might get into the interior of the button and insulate it so it doesn't work. You need sealed buttons. Some surface-mount buttons are sealed.[1] Many are not. I was thinking more from the point of view of what simple manufacturing step could the maker add to package the thing. Shrink-tube sounds good, although it might hold the button down if shrunk too hard.

[1] https://www.omron.com/ecb/products/sw/24/b3s.html

The sealed switches sound like good idea for the plastic dip.

I've done the heat shrink before with good success. If the button gets depressed by the tubing a quick cut with a craft / xacto knife around the button works well.

I'm not trying to make it water proof, just survive being banged around by all the pens / keys / USB / cables / power blocks / change / assorted other detritus that lives in the pockets of my computer bag.