I actually care more about the aesthetics of the speakers than the driver materials.
Titanium is about "middle" price range (a lot less than Diamond & Be), probably tougher and more durable, and I think Ti sounds & measure as great as Be and Diamond.
KEF Reference objectively measures better than Revel, B&W, and almost all brands. KEF Reference subjectively sounds as great as any of these brands. KEF Reference has Ti tweeters. There is no need for rare and exotic driver materials IMO.
I know the speaker companies want to tell everyone that the ONLY reason they pursue these rare, exotic, and expensive driver materials is because of PERFORMANCE.
But I don't believe them. It's mostly marketing IMO, like everything else in the world.
"Diamond" tweeters - exotic, Ooh, ah.
I would rather have a B&W 802T (Ti tweeter, Ti midrange, Ti woofer) for $9K, instead of $15K with the measurement of the KEF Reference.