Yes. Lately, between PF Savage reclears and Crystalline Conflict, I've found myself developing increasingly negative feelings towards my fellow WoLs. I wish I didn't, but that's just how it is. Hard solo content would allow me to take a break and still scratch that gamer itch without having to disconnect from the game altogether.
Bozja's a great example, as you mentioned. And it's done within the definition of an MMO. I always enjoy watching others duel too - getting the mettle buff is just a bonus. Would love to see more solo spectator content like that (that isn't locked behind a timer/RNG/grinding. Just make it lobby based.)
If done right it also allows high performers to develop reknown in their community without the need for ranking websites. "Hey, Biggus Dickus is soloing Thordan on Omega, wanna go watch?" Very MMO.
As for the healer problem... tune the content for DPS, healers adjust. You know some crazy few will still pull it off.