I didn't modify the archers too much, just added heads from the viking and saxon boxes to a few of them. Most of them got helmeted heads though.
The rest of the infantry I mixed up more, adding heads, arms and bodies from the viking, saxon and dark age boxes. This turned my 44 Romans into 67 finished models, two 12-man units of armoured guys using the armoured body and vikings and saxons, one 12-man unarmoured unit using just the models from the box (with additional heads), and one 12-man levy/limitanei unit with a few bodies from the box and the rest dark age warriors, all with round shields.
I agree that the box itself is limited (the cloned helmet heads is my biggest complaint), but it gains a lot from kit-bashing.