You may want to try and understand what caused the problem so that it doesn't catch you unawares later.
I think I've finally solved it. When I run the portable Bitcoin-Qt (the .zip download), I was not getting more than 8 connections except for the above one-time connection number of 13. I later ran the .exe version instead and I now get consistently 20 or so connections.
My estimation is that because the portable Bitcoin client was not running from the default location, the automatically created Windows firewall exception did not apply to it, because the firewall exception was probably pointed towards the "C/Program Files" install path for the client. When running the .exe (after it performed an installation procedure), the client was then running from the expected "C/Program Files" location and therefore the Windows firewall exception began working as intended. I could be wrong.