The so called "Xenon" bulbs really don't produce much more light than a standard bulb at the same wattage, but because the bulbs are painted blue, the light appears more white, giving the illusion that the light is brighter. This is basically the same concept with a lot of the garbage Xenon headlight bulbs.

In the case of the 5 watt "replacement" instrument cluster bulbs, there really is no miracle here. If you change a 50 watt light bulb in your living room to a 100 watt bulb, I sure HOPE that it produces more light. You can probably achieve the same (if not better) effect with standard clear 5W 194 or 168 bulbs.

The OEM bulbs are 3 watts and a 5 watt is close to double the output, so I'm sure that it does produce more heat. I suggest going with LED's.

PS: The previous owner of my car had 5W 194 bulbs in the cluster. The area around where the bulb sits (lighting channel) was a bit melted. I wish I had it here so I could take a picture of it. I replaced the cluster with that from a 1995 E320, which has better designed lighting channels, resulting in MUCH better gauge illumination over the previous (86-89) models!