Manual portals would give me reason to use WED ^^ Most times it's unnecessary to wait for a long compile time to have culling between a few rooms (unless they each have a LOT in them), but to be able to set out the really important occlusion portals by hand would be fantastic.
DX 11 will bring you only advantages if you really use it's features, if you support real-time tesselation, global illumination, deferreed lighting or ambient occlusion. Otherwise you can do like id-software and just stick to DX9.
I agree -- DX9 is/was a milestone in graphics that can still be taken advantage of for more advanced effects than we've already seen (with shader model 3.0, practically the only thing limiting us is the speed of the graphics card) -- my interest in DX 11 lies almost completely in DirectCompute -- I went to a CUDA seminar last year and loved what I saw and heard, and it was all very straight-forward, but an enticing part of DirectCompute is compatibility -- presumably, a card that supports DX 11 supports DirectCompute.
Jibb
