I upgraded mine to a Philips Vision Plus xenon bulb - again, a big difference, and since it's the same wattage no mods required. Cost about a tenner. Also good for winter as it's dual colour - dip beam is a slightly yellow tint, better in foggy or damp conditions, high beam is blue white and superb, good beam pattern as well.
Keep to the standard ratings and the electrics need no modification. The difference is down to the quality of the components in the bulb... they still only draw 55W......... I run the Halfords 30% % 50% brighter bulbs.... I think they may have a BOGOF offer on some of their range at the moment.