From that era, I think Sufjan and Joanna Newsom are probably the two that actually were able to leverage real careers. I think some Sufjan is great (Illinois, Age of Adz) but I never actually finished listening to Carrie and Lowell. But I think Joanna Newsom is better than basically anything else.

I guess Of Montreal and The Decemberists have managed to eke out decent careers, but from my perspective they both never came close to replicating the Good Early Ones and should have quit in 2005.

Fiery Furances are probably the big one that completely fell off. I just checked Spotify - Decemberists and OM both get around 800k listeners per month, FF are at 20k. I still love them, but they were always going to be a tough sit for most people.