I have an uprated headlight loom on my MK2 16V and run 150/100w in the normal lights and 150w in the driving lights, never had any problems with MOT's and is funny as you like when people come towards you with main beam on to put mine on, Its like having football stadium lights on the front of the car.
As for water in the light theres only one answer for that, water is getting in, theres a rubber boot on the back which needs to be fitted properly, Take the light out and blow it dry with an airline to get rid of the mist.
The upgrade is fairly easy to do, you just use the standard wiring as the relay switching feed and take the power for the lights direct from the battery. So you don't get voltage drop.
I know a web site with a wiring diagram thats well good, I'll put a link to it on here.