I feel obligated to call into question your definition of "human" (homo sapiens have certainly not been around for more than 500,000 years, and that number is itself exceedingly high) but that's totally beside the point, so I'll refrain.
To address your point, tho. Why would the numbers matter? Do you believe that human worth on a spiritual level is more valuable when the species population is smaller? When the population bottle-necked 70,000 years ago, were those 10,000 breeding pairs of humans spiritually more important than are people in the year 2014, assuming that the only determining factor is, as you're suggesting, the number of people on the planet? Obviously, they were worth more genetically and biologically. But spiritually? Assuming that a God, gods, or some other super-, sub-, or para-natural entity created the earth and humanity, does it actually make sense to you that such a being would care more about a small population than a large one? That it would be bothered at all by the process of differentiating those many entities?
And, hey, why does it even have to differentiate? Many religions teach spiritual meaning through unity. Individuality is an illusion; but the spiritual implications are no less substantial. If I'm really just a single, tiny drop of water pulled from an ocean or suspended above it, does my substance actually change? Is there any less of me?
I don't believe that the vastness of the population or the vastness of our planet or solar system or the universe are a threat to my spiritual being. Spirituality doesn't really give a damn about numbers.
As for the question of heaven and hell...do you really believe that those are viewed as finite places with a seating capacity, or that souls actually occupy a quantifiable space? Heaven and hell are neither spaces nor states of mind; they're states of being.
Somewhere, something incredible is waiting to be known.