2 days in after a 4490 upgrade from the Uber. There is definitely a noticeable difference over the Uber. Not to abuse terms, but instrument separation is noticeably better and music sounds much more natural. I found the Uber to have a bit of bite in the some top end that sometimes made cymbals and vocals sound a little... too metallic? The 4490 provides a nice smooth reproduction. I'm quite happy with the bump for the price and I think I'll be passing on the Multibit option for now an let my ignorance be bliss.
4490 is, without a doubt, worth $70 for Uber owners if you got a few bucks to spare. Not sure if I would say the same if it was much more, however. The differences are noticeable, not mind blowing.
If the Multibit upgrade is too much for you to swallow (It equals out to $400 or so for us Canadians, 4490 was $100 or so) the 4490 is a pretty decent $70 bump IMO.
MacMini->256k to ALAC->Bifrost 4490->Schiit Valhalla 2 NOS tubes->HD600
Edit: For those curious, because I was concerned, install is easy. If you've taken apart a computer before, theres nothing to worry about. Theres a great tutorial on how the upgrade goes in the Uber thread.