Well stated Geoff .... and I like your philosophy of "solid, straight and simple" ... because that is what is humanly controllable during the putting stroke and subsequent impact event. After the ball leaves the putter face it enters a random world of chaos, bifurcated by an errant blade of grass or divot repair.
When you state: "We need some data about the difference backspin makes on the line of the putt." .... I would add that the mysterious coefficient of friction between the moving ball and the grass surface may supercede any consideration about initial ball spin direction. Surely the grass surface is too variable and the vagaries of grass blades and ground are too significant for anybody to neurotically worry about initial post-impact conditions.
If one can better one holed putt in four from 10 feet, one is a statistical winner ... and I don't mean four consecutive putts from 10 feet ... I mean four putts on four greens separated by fairways ... or ... four putts at 10 minute intervals ... you know what I mean ..... !!!!