The main reason to change the thermostat is because it'* running too hot or too cold, or if you want to lower the vehicle operating temperature. Other than that, I say if it ain't broke, don't fix it.
And I have never given any thought to the 2 fans thing. My guess is air conditioning mainly. I have noticed in my Park Avenue, there is a main fan, and a secondary fan. The main fain is bigger and heavier, has 2 speeds, and is shrouded. The secondary is single speed, not shrouded, and runs whether the main fain is on low or high. It also depends on the car. If you are talking about RWD cars with the engine driven fan, the fans are usually sized and shrouded accordingly.
Another useless tidbit, my Regal has 2 fans also, only near as I can tell, they are both single speed, and it uses 1 fan vs 2 when the PA would be switching the main between low and high.
I would rather have too much fan, than not enough anyway