I know what you mean!
The exact same thing happened to me with my R53 back in 2004, 18 months after I took delivery. The rears went first, costing me over US $500 to have replaced at the dealer.
When the fronts went later that year I fitted after-market rotors (slotted) on all four wheels with Green Stuf pads for about the same price. I drove those brakes for another 100K+ miles so I considered them a good investment.
They were pretty well shot at 133K when I finally sold that MINI. I just today bought a set of EBC rotors & Green Stuff pads for my R56 as I have 16K+ on as of today.
If yours only lasted 18K I 'spect mine aren't too far behind thought they didn't look all that bad (maybe 5mm pad left front & rear) when I mounted up my winter rims & tires a month ago.