Cartridge bearing headsets definitely are nice but worth the expense? I don't think so. My Brompton still sports it's stock headset after a couple of years of riding in good weather, rain, sleet, snow and hail. It just works. Even my Bike Friday which sports cartridge bearings in the headset, wheels and bottom bracket still needs routine maintenance (not to mention that the externals of cartridge bearings need to be kept clean, especially BBs which I've seen fail after only a year when allowed to remain dirty) and cleaning/lubing/adjusting a 'standard' headset would add very little time to that. So AFAIC a headset is the last thing I would change over to cartridge bearings if I ever wanted to improve my Brompton... especially at ~$125 for a CK.