I blacked out my lights, and I regret doing so, but not nearly as much as people seem to think. The blackout spray doesn't really block much light coming through, what it does is make the lights look blackened, while still letting them shine fine when on. I may have lost 5% brightness. I just, in the end, don't like the look as much as I thought I would. If I had it to do over, I'd mask the lights themselves, and just spray the chrome and so forth.
On the other hand, I also blacked my tail, and I like the effect there a lot. Again, whenever the lights are on they show just fine, but when off they look black instead of white. I masked the red, since that was the look I was going for, and I like that look... and I think having done so makes me a little less a target for the law; pure black is obvious, but black and red reflectors, maybe not so much. Anyway, knock wood, I haven't been pulled over so far.