Latest update:

I've got 19.5K miles on my Michelin PS2 tires and I had them checked this past weekend at the America's Tire store that has always taken good care of me. All of them still have 6/32 inch except for the right front that has 8/32. I had him check on availability and there's no problem getting the 18" front -- 26 at a nearby store -- but they only have 4 in stock of the rear 19" tires...still not low enough for him to worry about (I offered to prepay and buy the tires now so they would be sure to be available if I needed them). The two different tires cost less than $350 and $250? (I can't remember exactly...$327?...but much less than I thought based on some old posts).

Don't need new tires yet...he thought I had another 4K miles or so more to go.