if changing your fogs to spotlights make sure you change the wiring over to be legal.
However if using HID on your non HID car, bear in mind that is illegal. In Kent and essex police are now clamping down like mad as many accidents are now being attributed to oncoming traffic blinded by illegal HID kits.
Also can i just make one thing clear. Xenons are not the only option. My last three cars ( mini's ) came with Xenons standard, and they were not any better than a good set of halogens.
So a cheaper and better way for most would be to upgrade to something liek nighbreaker bulbs which are superb. i'd then look at putting some 100 watt bulbs in the foglights and then wiring these up as spots. But you may want different lenses to get the distance.
I still think the best lights i ever had were the upgraded Spotlights on my mini, they were superb on the back roads at night,
I dont want to use my foglights as spots. to start with, thats illegal (cough cough) and I have no need for the extra lighting. I've had Nightbreakers, and Phillips extreme, and I've been running HID in my dipped beam for over a year now.
I honestly doubt that I'll ever really use the fogs TBH apart from photos and (shock horror) fog. Even when its foggy I dont really use my fogs, but you need the fronts on for the rear to come on.
Like I say, I got a good deal on the kits, and I have considered doing the main beam for a while.
Being able to see further is never a bad thing, and I certainly dont plan on dazzling anyone.
My current HID set up is a lot brighter than the phillips extreme they replaced, and yet, dont dazzle anyone as far as I'm aware. Certainly not as much as I get dazzled by people with standard lights that are badly misaligned, or by idiots driving in the snow with fog lights on.