But you’re right when you say that the 3.0 + books still have value. I still use the Arms and Equipment Guide, the Stronghold Builder’s Guide, and the Ghostwalk Campaign setting, among others. Just because you start to play a new version, doesn’t mean the old stuff has to go away.

I’m a big Forgotten Realms fan and I have been playing 4e in the Realms almost since the week the 4e books came out (and months before the 4e Realms books).

Using my 3e setting books I was able to play a 4e Realms game seamlessly. I had to do VERY little retconning when the 4e Realms books came out (in fairness I had some knowledge of what the 4e Realms would look like ahead of time).

This is an indicator to me that 3e setting books should be easily convertible to 4e rules. Since we already have full rules on Warforged as a race and Artificer as a class (on DDI), and a Monster Manual version of the Shifter as well, there is little reason that your 3e Eberron books shouldn’t be fully convertible into 4e as well. The only thing it’s missing at this point is psionics, and that can be worked around pretty easily.