Since your are posting in the Harrah's forum, I assume you are looking at CET properties. I do not know much about Harrah's Reno other than the downtown is nothing special. As to Lake Tahoe, I prefer Harrah's over Harveys because every Harrah's Lake Tahoe room has two full bathrooms - apparently at the insistence of Bill Harrah. Harrah's and Harveys are connected by an underground passage (under Hwy 50) so you can dart from one location to another. The Diamond Lounge at Harveys is quite scenic but you need to take the "golden door" elevator to get there and may need to page the elevator operator - don't forget to tip a buck or two.
There is a good late night breakfast available at the bar next to the Harrah's buffet -- it is brand new.
There are three steakhouse style fine restaurants. I like the Sage Room off the casino at Harvey's as I like the wood paneled, table cooking service available there. But Friday's Station (Harrah's) or Kitchen 19 (Harveys) have nice scenic views. Don't miss the buffet on Harrah's side as it has the best view of any buffet I have ever seen. It overlooks Lake Tahoe and the mountains.
If you are going in Spring (and there is no snow), I suggest you rent a car at Reno airport to drive to Lake Tahoe. If you can talk your host into a limo, that would work as well but then it is hard to get around and see Emerald Bay unless you take a boat ride. Diamond holders can get a complimentary boat ride on Lake Tahoe if available that time of year, ask a host to set that up.
There is a CVS drug store and Raley's supermarket walking distance from Harrah's or Harveys in case you need something. It is fun to check out the shops toward the California side.
Lake Tahoe is a slice of heaven.