Here at the office they recently did a refurbishing exercise. It included painting most of the place and cleaning the carpets. Reasonable. They also did work in the toilets. They didn't replace the toilets. They did, however, replace the seats and the locks on the cubicle doors. This has proved very effective, since these are about half of the user experience that a toilet can offer. The majority of what happens in the toilet, and what happens in the toilet stays in the toilet - a phrase which reminds me of my recent battle with blockage - the majority of what happens is actually a matter between the user and his digestive system. However, assuming a suitably cleaning regime, there is not a whole lot you can do to improve the usability of the toilet. Some other possibles include stopping the toilet roll from jamming and making the flush a bit more effective.

So a toilet has a user interface. Seat, door, roll, flush. That's all.