An interesting, if somewhat tedious thread at times.  For myself, I always renew my passport 6 months out as the general rule appears to be that many countries require that 6 month validity.  BTW Dazza, thanks for the link to TIMATIC, I have saved that.
As an aside, I do not travel frequently, only as and when finances allow.  However, I don't like unnecessary grief, and try to have all bases covered - just in case a nice opportunity came up for me to go somewhere.  I am not flush with cash, but the loss of a few dollars renewing my passport early doesn't faze me one iota.  The cost of peace of mind - PRICELESS.