The trick to impossibles is keep them within a short range (few hundred tops) of one another, and let the top 10~20 bank up UDLs like mad while questing out the rest of them. (Heck, when I was maxing INferni, she banked over 400+ UDLs before she maxed out entirely, and I had at least 10~15 ponies with 100+ UDLs on their own, and that was WITH questing them through a hard quest each round. They WILL build up.)
As it stands, I wish I knew if there was a reason, outside "just collecting" to have them. (Or maybe future "forging" recipe? As a turn in method, that is... Hmm...) I dunno, I don't know if I should feel compelled to do it. For item collection's sake only? No. I don't feel like killing myself yet.

Still cool though, I can see myself shooting off the occasional one to get the item for selling maybe.