My wife and I attended the nighttime walking tour last week. It was fun and informative. Our guide provided lots of history of how downtown has developed and changed (development often very quickly and without regard to preservation) along with key personalities that made it all happen. Lots of stories about risky land deals, big successes, spectacular failures, missed opportunities, and urban renewal.
The nighttime tour competes with the noise and activity of Fremont Street, but the amplified, wireless earpieces help considerably. Lots of good tips on places to stay, east, ad shop. Highlights for us were the shark tank pool at the Golden Nugget and the Fremont Street east redevelopment area.
We would highly recommend spending a few hours of your las Vegas trip on the tour.