Handbrake relation to disk wear
 

My R53 Cooper S has got handbrake issues - that is, it doesn't work. I've tightened the adjuster as much as it will go (and even put a couple of bigger nuts under the adjustment nut to shim it out), but it does't work for sh!t. I took the rear wheels off and noticed that the rare disks are pretty worn, and the brake warning 'error' light is on. I'm wondering if worn disks would affect the handbrake?
As much as the rear disks are worn, they look like they've still got plenty of life left in them. Is it worth getting an OBD2 tool and trying to reset the warning light?