hmm couple weeks ago I changed out my gauge sensor(by headers) with a cheapo generic one(since the connector is a retarted design...) The gauge went from reading ~200 to 220. It does not hurt to replace a thermostat, however I would get another method to read the temp besides just the factory DUMMY gauge. I assume the sensor is just dialed in a little off, and basically jsut watch it to see that the engine is warming up, and that it doesnt spike up.
No engine runs a a constant 200-210*. if they did the fan would have to run nearly all the time, and something more precise than a thermostat would be needed. If factory engine temp gauges were accurate people would panic their vehicle was over heating every time they stopped, or think it was running way to cold whenever they are on the highway. My CBR that redlines at 16k, runs anywhere from 170F to 220F(fan kicks on), fully warmed up, it just depends on the engine.
EDIT.
Theoretically an internal combustion engine will operate more efficiently the higher the temperatures, however when you add in expansion and contraction of the engine, air density, fuel detonation, oil, coolant boiling point, etc, there is a limit to how hot you want to run it.