Metropolis, Tower of Babel, Big O
What if the series is a major symbolic tale of the cycle of humanity? What I mean is in relation to the story of Metropolis and the Biblical story the film itself refers to which is the story of the Tower of Babel which humanity attempted to build to reach the heavens and God only to have God destroy it and divide humanity with countries, languages and other barriers to slow or completely stop their progress in trying to reach the heavens.
In Big O, you have various people trying to search for the "truth" of what happened 40 years ago as well as the "perfection" (in other words, unification of humanity) through the "red tomatoes" from Gordon Rosewater, and not to mention Alex Rosewater's attempt to achieve God-like status. Then of course, at the end of the series, just when the truth is close to being fully revealed (with Alan Gabriel/Schwartzwald reaching the lamp light sky/heavens, Angel's origin with the tv filming set, Rosewater and Smith's own revelations) does humanity once again become divided by the foreign nation organization (Union) with their foreign megadeus and Angel returns in the Big Venus to restart the world and wipe it clean of progress, returning it to square one.
The intricate details of Big O may not be important when thinking of the series this way, although this theory is hurt by the fact that they had more episodes written for another season or two.
Thoughts? Additions?