If they're old-style halogen bulbs, the can be replaced by high-intensity versions - Philips Xtreme or Osram Night Breaker have good reputations - they won't damage the electrics as they're the same electric power, 55w.

If they're new-style 25w HIDs (not the usual 35w HIDs) you're stuck with them unless you change the whole headlight, ballasts and other wiring - you can get 35w HID "bulbs" but the fitting is different on the 25w.

There's quite a few complaints about the halogen headlights on astrakforums.co.uk. The Matrix headlights are apparently superb but as long as they're a £1k option they will never be popular.

You can get a decent 35w HID kit for £70 but the legality of them is still a grey area, but as others have said Nightbreakers are a cheap and easy upgrade.