As John noted, you can get brighter bulbs for your Euros instead of rewiring your system. There have been significant advances in the amount of light these normal 55w H4 bulbs put out since they were originally introduced.
Go for the +30 ones that John uses, or you can go even higher with the +50 Philips Vision Plus that I'm using now.
The claim of 50% more light than stock is accurate. These bulbs are bright!