Hi there John Aquila,
My two cents.
How about this: What if its a natural part of the evolution of religion?
What do I mean by this? Well according to Prof. Bob Briar the ancient Egyptians only believed that the Pharaoh's had a 'ba' (The personal characteristics that remain after the individual dies that ascends to the heavens). Everyone had a 'ka' or life force. Later on the religion evolved that lower royals also had a 'ba'. Later tradesmen and professionals claimed the same and then finally every-man. This can be seen because in early dynasty's only the Pharaoh's had pyramid tombs, later lower royals and professionals and so on (The pyramids grow smaller in size too :)) The liberalization of the culture over time caused a view of equality in the afterlife (Not that the slave is equal to the Pharaoh in the afterlife but that he actually gets to have one) . Also see: Ian Shaw - The Oxford History of Ancient Egypt (2000) p180-181 Callender, Gae, "The Middle Kingdom"
What I'm getting at is that Christianity represents an evolution of the Jewish tradition. There are two mentions in the Old Testament that elude to possible heavenly ascents: Elijah and Enoch. Both have special status: One as a pre-flood patriarch and the other a profit. Perhaps the germ of an idea. Heaven originally viewed as an exception for the exceptional or the very special but later becomes a destination for all. Perhaps it could be viewed as an equalizer.
The Gospels I view as the evolution of a philosophy which emerges out of the Jewish culture. Not the work of just the four gospel writers, but the work of a rebellious component of the Jewish community creating a new liberal tradition. The sayings of Jesus were being passed around very early and that those sayings also multiplied and evolved as can be seen in the Gospel of Thomas (which may be the oldest recorded sayings of Jesus 40 ce or much much later140 ce). Whats important is not the dating of Thomas but that sayings of Jesus on their own were being passed around, and when combined with anecdotes about Jesus or persons confused with Jesus became the basis of the four narratives. Mark is the oldest and may be based on Thomas. Matthew and Luke borrow from Mark and John is the odd one out who adds totally different ideas (like the Deity of Christ)
Heaven liberalizes the Jewish community. The class system is effectively destroyed in the afterlife through the Gospels (I'm ignoring anything beyond the gospels for the sake of argument). The community who evolved the Gospels probably drew on the possible allusions of Elijah and Enoch and combined them with other ideas coming from Zoroaster, Egypt etc. I also think of it in terms of the evolution of the JW faith. In Russells day everyone went to heaven. Later J F Rutherford alters the tradition and emphasizes the class system with two destinations. The whole process takes a couple of decades, just like the evolution of the Christian tradition of heaven.