Unless you cut it with a knife or something I doubt your fermometer is broken. They are fairly inaccurate though. I "calibrated" mine using a scientific grade digital probe type thermometer and noticed the reading to be the lowest color changed area on the strip, but I suspect they are all different. Also, you are reading the temperature of the outside of your fermentation vessel. I'd assume it would be at least a few degrees warmer on the inside. All that said, depending on the efficiency of your swamp cooler setup, 72 degrees during active fermentation with swamp cooler water at 46 doesn't sound that crazy to me.
As for your second question, I'd say widely fluctuating temperatures are generally worse, assuming you're not talking about excessively high. Each yeast strain has a recommended temperature range and some, like many Belgians, actually do quite well warmer than even the upper limit. A good "temperature profile" in general is to start the beer as close to the lower limit as possible and keep it from exceeding the upper limit for at least the most active portion of the ferment. As it winds down creeping the temperature up another degree or two can help with attenuation on strains that tend to quit early...