Thinking of fitting an HID conversion kit in my motor, does anyone have any experience with these? Are they worth it? How much is reasonable to spend on a decent kit?
Don't. Unless you really know what you're doing then it's easy to end up with lights that don't improve your visibility but dazzle oncoming motorists. Headlamp beams are now tested as part of the MOT and you'll fail if the beam isn't correctly aimed and focussed, which is why most HID kits are advertised as "for off-road use only" - the manufacturers know that the kits won't pass an MOT.
The best lighting upgrade most people can make is to fit LED brake lights. They reach full brightness about 200ms quicker than incandescent bulbs, which could save you from a rear-end shunt.