Dave,
Thats interesting about the 3lb blanks..because I well remember the cost of the blanks way back in about 1985/86..they where £43 each! £7 in 20+ years aint too bad
I use cane and fibreglass blanks for stalking carp, and the reason is the action. It bends and bends and you just clamp up on the centrepin and hold. They will stop fish in there tracks without locking up or exploding
For years I used 1.25tc rods from North Western and they where a dream to play carp, tench and barbel on. I then stepped up to the 1.75 version for bigger carp. In 1910 I got a pair of the Carbon versions of the 1.75 and although they outcast the glass versions by some way, they just did not have that "feel" about them when playing fish.
As for glass fly rods, I think the advantage comes with short light line rods..say a 7 foot 3 weight. The natural weight of the blank allows the rod to flex more thus making short casts on small rivers easy. With a carbon rod you frequently have to arialise more line or over line the rod to get it to work close in.
I think glass still has a place in fishing, both fly and otherwise, as does cane.