The hose is usually the biggest issue. Another thing might be that the fan blades are dirty but that's something of a delicate job that I personally wouldn't try to tackle. Getting the motor out is a pain, and getting it back in with the fans properly aligned and balanced is an even bigger problem. Also, of course, make sure the cloth bag is spotless. Whenever I empty one, I always whap it against the side of the building to dislodge all the fine dirt. You'd be surprised what a difference that can make.
You guys should keep your eyes on eBay -- polisher attachments turn up fairly often. I think there are a couple of them running now.