Bunnycatz, I agree that it's a tough one to answer.
On balance, I come down on the side of having some form of activity that keeps agents brain switched on during wait time. Sitting waiting for calls to come in can cause brain death if the resource planning isn't right but even with the best planning external factors can still generate long wait times. It's been a long time since I was an inbound agent at BT which was a job that was, luckily, on a 3 week rotation with admin work. A colleague of mine knitted 4 jumpers during her 3 weeks on inbound and I did my day release college assignments, and wrote appalling poetry. Perhaps you might like this:
Slumped in front of my VDU
Wishing there was something else to do
Starring at white fluttering blinds
With my headset slowly killing my mind
Looking out of the windows, I can see
The roof tops of Wimbledon laughing at me
The trees are waving, they seem to say
'Come out, escape, experience the day'
But still I sit like an inanimate clone
Listening to the printers whine and drone
How much longer can it be
Oh Christ, it's still only 10:53