I had a similar problem with a set of floor lamps in my dining room. I scavenged the parts from other lamps when they first needed replacement. When the dimmers went out I converted them to fluorescent and have been happy with the results.

When I scavenged I searched thrift shops and found the parts. Later I purchased new florescent floor lamps and scavenged their parts. In my area Lamps Plus can usually get parts. My floor lamps, though purchased at Lamps Plus, were made in Italy, and the parts were ridiculously expensive, so I converted them.

500w is a lot, but if possible check the lumens the bulbs produce. The lumens rating may not be as high as 500w would indicate. Maybe a smaller wattage may produce more lumens if there is a choice of bulb brands.

It sounds as though you like bright indirect light. In my living room I have one main floorlamp and 3 lights that come on when the main wall switch is turned on. All of them are on independent dimmers. The "3 lights" are cheap florescent floor lamps that have had their poles removed, so they are just the upfacing light shade attached to a base. These sit on top of an entertainment unit and on a bookcase and aren't very noticeable, design wise, even when turned on. The room can be very very bright or dimmed for tv. They are all florescent so the total wattage in the room is low, I think less than 150w total. The lighting is also very even since there are 4 lights. Also, for comparison, my living room ceiling is 22 feet at the highest point.

Hope that helps.
-Hal

Thanks Hal; some thoughts & options I hadn't considered.