Any suggestions on a luxury hotel very convenient to the Kennedy Center? I'm going for one night and am willing to splurge!

How about none other than the Watergate? It's right next to the Center, and depending on your room location, can have a terrific view of the Potomac. I believe there are some terrific shops as well on site.

Last time I was at the Watergate, it was showing its age. I would head for the Four Seasons in Georgetown. A 5-7 min cab ride to the Kennedy Center and walking distance to every kind of restaurant and shopping you could want.
If you are staying on a Sat night, the FS has one of the best Sun brunches in town.

Even closer is the Ritz Carlton in the West End.

I think The Watergate is the way to go for me given that I'm flying into Washington just for an opera and then leaving first thing the next morning. That said, I'd appreciate more info on the hotel, particularly the rooms. Is it still a "luxury" hotel? What level of room should I request? Thanks.

Go to TheWatergateHotel.com and you can see the refurbished rooms. Weekends have specials of 149 per room.

I would prefer one of the rooms looking out at the Potomac and on a higher level cause during the week there's pretty good traffic around there.

There's a Four Seasons also in the area which has luxury suites available.