Dungeons are more difficult to explore in the dark, literally, and contain stronger monsters. Chunsoft also gave monsters aura abilities which temporarily power them up.
Spike, not Sega, will publish Shiren the Wanderer 4 in Japan this winter. Probably 2010 winter. It also looks like Spike is handling all of Chunsoft’s future titles. They just brought 428 to PSP and PlayStation 3 and have Extreme Escape: 9 Hours, 9 People, 9 Doors in the pipeline. Hmm… I wonder if that means Shiren 4 has a better chance of being localized. Atlus has a good relationship with Spike since they’re publishing Kenka Bancho: Badass Rumble and are working on localizing Shiren the Wanderer 3.