Washers are required by law because if your lights get all cruded up with sh1te then the light can 'scatter' and cause oncomming drivers to be dazzled! That's the theory, anyway!
Whan comparing prices of xenons on different cars be sure to compare 'like with like'. The GTI has bi-xenons where both dipped and main beams are xenon. It's actually only one xenon bulb, however, and the beam is adjusted by a 'shutter' from main to dipped beam. Many cars have mono-xenon lights where only dipped beam (I think) is xenon which is a complete waste of time!