Many old houses have very small powder rooms in them that can be decorated so that they look very luxurious. Bold colors, busy patterns and sparkling accents can make even the smallest of rooms look very luxurious.
One key is to paint the walls a dark color such as chocolate, midnight blue or a dark cherry. The darker the room the more regal it seems. Flocked wallpaper, especially if it is a pattern flocked with gold or silver is also very rich looking. Just make sure that it does not look too old fashioned as sometimes this sort of effect can make a room look quite old. Black and white flocked wallpaper can also look great if the designer has a flair for the contemporary; Vivienne Westwood makes a few nice wall paper patterns that look great in a bathroom.
Lavish wall sconces dripping with large crystals gives powder rooms a very opulent feel.
Go for shiny nickel and gold plated mirrors and side tables. Silver wastebaskets also give the powder room a more glamorous feel. Pounded metal also looks quite luxuriant. The idea is to mix gold and silver accents. Use bowls and perfume flacons filled with soaps and pot pours with silver bottles and other touches for a very rich effect.
Towels that are white look much more luxuriant than ones that are patterned. Get the thickest nicest hand towels you can find; the large the pile the better. Ones lined or striped with gold or silver detail can also be quite impressive.
The most elegant of bathrooms do not have much clutter. Look for bowls or cups made out of old sea glass or metal. White china also works in this type of bathroom but it is not as chic. Blue glass or red glass accessories make this type of room look impressive as well.
If you do have a bit of clutter then look for antique style jars with copper tops as are found at anthropologie. Anthropolgie also makes a great soapdish that is silver and shaped like a serving tray. For the ultimate in luxury you can creatie nstant ambience by adding a chest in a dark cherry wood.
One way to add instant ambience to a powder room is to put dimmer switches on the lights to change the mood. Nice smelling candles in black or white glass jars, such as the ones made by Diptyqe Paris, are also a fashionable way to add glamor to a guest powder room.