Thread Update:
I completed my one year trial run of detailed expense tracking. Success! I kept track of all expenses throughout the year. I stuck with my original plan more or less, and updated my spreadsheet mainly at the end of each month using copy/pasted credit card statements and copy/pasted checkbook spreadsheet entries (supplemented with an occasional manual entry for cash expenses or to split a big walmart/target purchase into multiple categories). The DW was receptive to this tracking effort, and diligently (with a roll of her eyes) reported to me all cash expenses more than a buck or so.
After one year, I had $10 in "cash" expenses that went unaccounted for. Otherwise, everything was categorized into some spending category.
For the curious voyeurs, my "essential" or "bare bones" spending ended up at $22,000 for the year and when I lump in some discretionary spending (mainly vacations) it was $26,000 a year. This is for a family of 4 (including 2 young children).
Not included in these quotes of annual expenditures were mortgage payments (they go away if I choose to pay off the mortgage), child care expenses (not necessary when I ER), and student loan payments (during ER, I think I will qualify as low income so as to avoid paying most or all of these loans).
My goal in tracking detailed spending was to figure out what I would be spending during ER on the basics. The answer there was $22000 a year. Then I need to subtract out some work related expenses (mainly auto/gas) and add in a bunch of stuff like health insurance (which may be cheap/free come Jan 1 2014), more fun/discretionary spending/travel funds, and amortization of big capital expenses like auto purchases, roof, a/c, etc.
Going forward, I'm committed to tracking my expenses in detail like this long term. It will help me refine my spending target for ER, and also to see "where is the money going". Not that we are spendthrifts, but there is always the chance that some spending will grow out of control.