For what it's worth, I had a rigger go up the mast this week and look at the sheaves, among other things. In his opinion there is no problem going straight to line with my 1985 sheaves. He recommends any of the new lowest stretch, either 3/8 or 5/16ths. When I do change my halyards I won't be using his $5/foot product, but something more in the $1.50 range.
My original halyards are still quite usable, although the line has swollen some. IWhen I make the change I'll put winches on the mast, a setup I prefer for shorthanded sailing.
The rigger's inspection revealed a deep crack in the swage of the top fitting of my port lowers. It was on the underside--I completely missed it when I was up there in June.
Both lowers being changed out today.