Offroad-Express

Just upgraded my H4 headlight bulbs on the Surf, using lights larger than 60/55 was out of the question as the light components are made of polycarbonate the Philips +80s are still rated as a 60/55 watt bulb but give theoretically another 15 metres more range and better light to the sides than the Narva +50s I had been using. Next step is to install 170mm HID Driving Lights to boost high beam performance.

I use 90/100W lamps in the Surf's headlights and have never had a problem with the plastic housing.

I had three different auto electricians advise me not to use anything larger than 60/55 watt and my bro inlaw actually distorted his Surf headlights when using a combination of high wattage and incresed voltage (at the lights) using relays.
We found the voltage difference between battery and the lights on mine was less than half a volt so decided relays wouldn't be required
we are now getting the same amount of light as a 100 watt bulbs but less current draw (5 amps per headlight bulb as opposed to 10 amps).
The Britax 35 watt HID driving lights are arriving next week and are supposed to have another 150 metres more range than the 130 watt halogens that I used on the Terrano, will let you know how they work out.

Have youlooked at an HID conversion kit, lamps replace existing lamps and kit uses existing wiring loom for turning on,hi lo beam etc. Just mount a couple of ballast boxes and connect to battery. I use a kit on the 80 and its a huge difference.

From what I've read the hi/lo HID doesn't last long? Mechanism dies or something.

I'm keen to do just inner hi beams (4 headlights on my 80) because HID lo beam would be a bit stink on oncoming traffic.

No probs with hi lo beam to date. Lamp is same 2 fillament as normal lamps. Lo beam is pretty damn low, high beam lights up the world. HID does have an odd effect on colours, refective objects become super bright and other colours appear washed out. When doing one of the night stages at Rotorua we had battery problems (along with the persistant winch problems that weekend) and ran on HIDs only, we couldn't tell the difference between still water surfaces and damp clay, took some getting used to.

I checked out some of the Aussie forums and it seems to get a good HID kit you are looking at almost as much cash as to buy lights with good quality components installed.
You can buy cheap kits on ebay for around a hundred Aus dollars but on the aussie forums there were a lot of people who were unhappy with them. Prices seemed to range from the elcheapo's at $100 to around $800 and quality seemed to go pretty much with the price.
I had heard about the colour difference but the attraction was with power consumption of the lights being so low.
I had 130 watt halogen driving lights on the Terrano with 130/90's in the headlights but the alternator would only last about two years before needing a rebuild.
I believe that we now have the same reulations for onroad use as the Aussies. This means you can have HID driving lights and if your vehicle has dual headlights you can have HID in the high beam but not in the low beam if however your head lights are a combination hi beam/low beam like most cars, you it is illegal to use HID.

how weatherproof/waterproof are the conversion kits, would the lights work underwater or water splashing around near the lamp?

The more expensive lighting kits seem to be okay for being water proof as long as all the connectors are given a covering of Silicone.
For on road use with combo hi/lo beam lights you would not be able to take the vehicle to a testing station for a warrant as they would most certainly make you revert back to the halogen lights if your vehicle originally had halogens installed. I made that mistake once of going to a testing station when I had the 130/90 halogens installed luckily I had a set of the old bulbs in the vehicle so no probs to change them over.The problem seems to be that a combo light on low beam with HID still throws a lot of light everywhere. I don't believe LTSA or VTNZ came up with this rule themselves I think it is more likely they just copied the Aussies.