Before we start, recall Classical mechanics is based on three properties of nature: mass ( in kilograms(kg) ), distance ( in meters(m) ), and time ( in seconds (s) ) and all else is based on definitions based on combinations of these.

For example:

velocity: v = meters/seconds distance per time
momentum: p = kg x v mass times velocity
accelleration: a = v/seconds velocity per time
force: N = kg x a mass times accelleration or Newtons
Energy: J = N x meters force times distance or Joules
Power: W = J/seconds Energy per time or Watts

Let's look at your original equation, E=MC^2, and use dimensional analysis to find out what it really means.

Energy's unit of measure (its "dimension") is the Joule, which is defined as a kilogram x meter^2/second^2, or to put it another way, mass times velocity squared. Putting it still another way, mass times accelleration times distance. This definition is deliberate, physicists did not do it arbitrarily, it was just realized that if you define the Joule this way the science of mechanics falls into place and everything works.

Since the C in the Einstein equation is a velocity (m/s), the dimension of E comes out in Joules, which it should since the term on the right hand side is in units of mass times velocity squared. It is important to remember that this doesn't necessarily mean its true, just that it is mathematically consistent. Just because something is mathematically consistent doesn't mean it has to be true.

Let's look at your next equation, with some variables renamed to match my examples above

I=W/(4Pi(m^2)) where I is "intensity", "W" is power, and m is the distance in meters. The units of intensity are Watts per square meter. The sun is a good example of how this type of equation is used. If you know the sun's power output in Watts, divide it by 4 Pi m squared and you get the solar power through each square meter at distance m meters from the sun. Usually you work this the other way, you measure the number of watts going through a square meter, substitute it for I and solve the equation for W to give you the solar power output (providing you know m, of course).

As for your original question, are these two equations connected? The answer is no. The Einstein equation relating mass and energy is the result of applying the the definitions of force, momentum, energy, etc in a relativistic, not a classical environment. They were then verified by actual experiments. The intensity/power relation you describe is just a result of the properties of spheres, it a geometrical result, not a physical one. Anthing radiating from a point source, whether it be light, gas, sound, electric charge or even gravity is going to "spread out" according to an inverse square law fashion.