How do they know it is heavily subsidized and priced far below an actuarially fair value?

I don't think they realize this. Recently in my area some flood maps were updated to take account of new data suggesting increased risks, with subsequent increases in the subsidized flood insurance rates. The affected households raised a hue and cry, enlisting senators in their cause, and many got the increases reversed. Nothing in the rhetoric I read suggested that they realized they were already getting a great deal; instead, here and in the Florida articles I read (where the government objected to the remaining insurer increasing rates after recent hurricanes), the unstated assumption seemed to be that the rates were 'unfair' and profitable.

Is it worth going to all the trouble of finding out?

A house is hundreds of thousands of dollars, and the disruption to your life if it and its contents are destroyed is profound. In some place like Florida, it may be more likely than not that in your lifetime your house will be damaged or destroyed, especially given the suggestion that global warming will increase the variance of storms (and hence the occurrence of super-hurricanes). I think it is worthwhile!