The wattage given on the fixture refers to the maximum that can safely be used. That will be dictated by two things: The internal wiring of the fixture, and the heat that it can tolerate.
In reality the additional 6W of the three 42W lamps that you are using is probably not going to be a problem, but it would be wrong of me to advise you that it's OK - you are drawing more power than the fixture is rated for, and so it is potentially unsafe.
Also, as you have noted, it's expensive ;-)
When this fitting was designed, it was probably intended for 40W incandescent tungsten lamps. What you seem to have there are 42W incandescent tungsten-halogen lamps (often simply known as "halogen"). They were probably be marketed as "energy saving", as they are intended to replace 60W non-halogen lamps, but in your case are using roughly the same amount of energy to give more light.
So, you will need to consider whether you need as much light as you are getting at present, or whether you can cope with something dimmer. Then there are three options:
Tungsten halogen lamps of a lower wattage. These will give you less light, and cost you proportionately less to run, but are still relatively inefficient. They are dimmable, and if the fitting is one where the lamps are visible (which isn't clear from your pictures), they are a point source with the "sparkle" that you are used to.
Compact fluorescent lamps. You could choose ones that would give as much light as you have at present, but with less electricity. They would cost less to run. In most cases they would not be dimmable, and they would give a diffuse light rather than a point source. Care would also be needed to find ones that fitted in the light fixture, since they tend to be larger.
LED lamps. A few years ago I would have said "avoid", but these are just becoming good for general home use, and I have a number myself. You could choose ones that would give as much light as you have at present, but with less electricity. They would cost less to run (although significantly more to buy). Depending on the model they might or might not be dimmable, and they might offer a diffuse source or group of "sparkly" point sources. As with compact fluorescents, care would be needed re the physical dimensions.
Beware when buying these, because there are an awful lot of cheap ones around that are dim, or have a nasty colour, or are fine for a few months but then stop working / go dim / develop a nasty colour. It's worth paying £10+ per lamp for a well-known manufacturer such as Osram, Philips, GE. Even from the reputable names there are still some older models that give a nasty colour of light, and it's not always possible to tell in from specifications - so buy one and use it for a few weeks to see how you find it, before spending money on more.
My first choice would probably be the LED option, given the caveats above.