Agreed.
Wear factor is definitely a consideration.
Durability depends on the type of paint.
For example, the Happ 1p,2p,3p,4p buttons are painted, and most laptop keyboards have the letter painted nowadays.
For computers, I've used plastic primer with spray paints and have had good success.
The UI buttons won't get as much wear as the normal game buttons.
Expoy paints are quite durable and can be brush applied if the button is masked.
Your suggestion for a vinyl sticker on top is a good one.
Thanks.