I'll also let you in on a little secret... metal domes seem to match the sound of high end headphones better... and headphones are what most recording engineers/producers are using to finalize the recordings we hear. I've had better results in good sound by trying to duplicate a recording and recording techniques than in trying to recreate live music.
That is quite the blanket statment. You are assuming all metal domes have some characteristic "metal" sound. This is simply not true across the board.
You are further assuming that high end headphones all sound similar. They do not. Listen to my ER4s, my Grados, and my Senns and then tell me they sound the same (they don't).
Most engineers/producers worth a **** do not use headphones alone to evaluate a final mix. Headphones have poor reproduction of staging cues unless the music was recorded specifically for reproduction on headphones (binaural, holophonic, whatever term you would like to use), and the low freqency reproduction of headphones does not touch that of decent home stereo.
Studio monitors were designed specifically for the tasks you are alluding to.
Hell, a few years ago, Abbey Road studio had 5 B&W Nautilus 801s as their studio monitors. While they may not be the best speakers ever built, they sound ****ed good (yes I have personally heard them albeit in only a 2 channel setup), but they are a very far cry from any headphones.
With regard to your comment about install locations, this is exactly what I was talking about when I mentioned dispersion characteristics. Go grab a Hiquophon OWII and stick it in your kicks, I bet it would sound ****ing great if they weren't pointed right at you. This is largely due to their tremendous off-axis performance.
The same tweeters might sound horrible in a-pillars because the wide dispersion would create a ton of unwanted and potentially annoying reflection off the glass and dash. Meanwhile, a big aluminum tweeter with narrow dispersion could sound great in the pillars and horrible in the kicks.
While material is obviously something to consider when looking at a tweeter, it is important to remember that there is so much more to a tweeter than the dome material alone.