@simons-photography: That is probably what he meant. Dont think debri of stars consists as rocks in form of rocks, by the way.(Probably all gasseous at novas)
@Jesus: Not all planets have the same consistency, just look at our solar system for that. The various elements is not very uniform in the galaxy either. Older parts tend to have heavier elements.(of course)
The estimate of the plain number of planets the easier thing to guess, i think. It is damn hard to estimate the ammount of life there are shitloads of problems. Like, radiation levels, meteor strike levels, how many planetary systems are unstable.(Including planets coming by that are not bound to stars, messing with orbits.) Initiation of life chances, climate stability.
Given these, think heavier planets may actually have more life. They dont change orbit that easy, their shear size and thick atmospheres may protect life against radiation and impacts. Also attract them, but continuity of impacts might actually help evolution in adapting to them. Colisions with larger planets is unlikely, it is the sheer number of smaller bodies that make impact likely. (celestial body size versus counts is a log-log scale)
It is even harder to estimate chances of intelligent life, too.

But we have not seen alien cilivizations, and even with a very smal percentage population growth, the space they would need would fill a galaxy within a billion years.(I should check that)