we had this discussion several times and i definately see your point.
i think it all comes down to how you see asamoah on the left. personally, i do rate him quite highly. he´s fast, has good positioning, very good technique and passing and it´s very hard to go past him. of course he isn´t a player who dribbles past defenders all day long but are criscito, kolarov and santon those players? no...
if we want more penetration on the left flank we should go for another formation, not switch our LWB. btw: i absolutely agree that his best position is CM but if i had to choose between
1) asamoah starting as LWB and nainggolan being vidal´s replacement (up to 18mio?) and
2) asamoah moving to CM and kolarov/santon playing LWB (last number i read on kolarov were 12mio + high wages)
i would go for 1) in a heartbeat (considering 352!)...
criscito though...

. (more suited to a 4-men-backline i guess)