This was my take:

http://www.headforpoints.com/2014/06...s-point-worth/

Effectively, I will not pay over 0.75p (1.3c or so) per Avios. I won't lose money at 0.75p but, at the same time, I want some 'profit' on top to reflect the illiquidity.

If the spend helps you trigger a 241 then the dynamic shifts a bit.