Impossible to quantify at the moment, I'd say. You can probably get Silver for just over £1k (£1.67 per TP) if you're meticulous and have just about unlimited flexibility. On the other hand, 200 TPs via the Amex offer is probably the most inefficient at £25k.
So, anywhere between £1.67 to £125.
We will find out for real what BA thinks they are worth when the inevitable happens, unfortunately.