ever considered crytek's cryengine2 for interactive archvis?
cryengine 2 has some more advanced dynamic lighting features with convincing realtime shadows and even some realtime ambient occlusion which really improves visual quality a lot.
a french company IMAGTP
http://www.imagtp.com/uk/ had already licenced cryengine 2 for realtime visualisations and their results so far are really impressive. look at their yacht-show-video. the realtime shadows are really stunning, and there is nothing prebaked. also have a look at their demoreel:
http://www.imagtp.com/videos/IMAGTP.mov
i think the subtle light/object interactions are the most important factor for making a visualisation more life-like. although cryengine 2 doesn't support any realtime GI-lighting, the approximations with ambient occlusion etc. are already a big step forward in visual quality compared to the other 3d-engines.