I always contribute my $0.02 and then some when it comes to lighting. Having mostly silver cars, I've taken great pains to find what lights work for spotting defects. With the right light, silver can show marring just as well as black (clear is clear); the trick is to find the right light.
Yeah, don't expect fluorescent to show defects. My cars look nearly perfect under fluorescents *before* I polish out the marring. Look OK under halogens too. But if I turn out all the other lights and then turn on the incandescents, at just the right illumination/viewing angle they look like a horrorshow- the previously invisible marring suddenly appears very bad.
I find that regular (but high wattage) incandescent lights work even better than halogens for really fine inspection. Even though I use halogens when I polish, I always do my final inspection with incandescents.
IIRC, when Mike Phillips tested Metal Halides for Meguiar's, he was less than impressed with them. I don't recall the specifics, but the discussions we had about it persuaded me not to bother with them. Not like they aren't very good or anything, but for me it's a matter of functionality. I can see what I'm looking for or I can't, and I don't see any reason to spend money unnecessarily any more than I see any reason to skimp on lighting and miss seeing something.
Before you spend/budget a bundle on Metal Halides, get enough light to cover the basics- be sure you have enough fluorescents for general illumination (including some on the walls) and some portable halogens (so you can direct light where/how you want it) and at least an old-fashioned incandescent troublelight for careful swirl-spotting.