If you're going to wait for your original pads to wear out, you'll be old and grey. The oem pads wear like iron. You'll probably get over 100K miles out of them and change them at that point out of guilt and not necessity
This kinda sounds like my Kenda tires on the front... 19K and they look like they got another 19 K to go!
Thinking about replacing them when I get a new rear tire... the Cooper is about worn down to the wear bars now with 11K miles on it.