Its visibility was even more striking because there were clouds floating around (i.e., its exceptional visibility wasn't due to it merely being the only white thing in the sky) and a cloud slightly covered it.
Additionally, over the summer, I saw the Moon regularly around an hour before sunset.
Of course, there could be practical reasons for it:
1) The Moon is closer to the Sun (enabling the Sun to illuminate it more).
2) The Moon is closer to the Earth.
3) The Sun is shining brighter, making the Moon (and other planetary bodies) brighter.
4) In addition to the Sun, another luminary body (Nibiru!) is shining on us all, making the Moon (and other planetary bodies) brighter.
Most of the above can be checked out online.
However, there are also always spiritual reasons for naturally occurring events.
We know that the Jewish Nation is compared to the Moon.
It seems that if the Moon's light is growing brighter, then that is a good indication that our light is growing brighter, too.
Furthermore, our Sages speak of the Sun and the Moon possessing separate "memshalah" - authority or rulership - the Moon's memshalah occurring at night while the Sun's memshalah occurs during the day. But now the Moon is increasing its memshalah by edging into the Sun's memshalah, which is also a good sign for us.
And even if this was only a one-time occurrence, the fact that it occurred Erev Yom Kippur is still significant.
Finally, many others have already noted that the Moon has become very bright at night and at times, we've seen an enormous and very beautiful halo around the Moon.
I really hope that the Moon's increased light and memshalah is truly a siman tov for us.
May we merit that it be so.