Funnily enough, I've been thinking about trying something like this. Because I'm so sick of GW's prices, I've decided to start SAGA (a Historical Dark Ages Skirmish game) and bought around 86 assorted Anglo Saxons (for less than £50 too!). I also intend to use them as Rohan Infantry at some point, maybe the men of the Westfold (led by Grimbold) . 86 miniatures gives me a lot of Rohan shieldwalls.
And as a bonus, Gripping Beast does very cheap metals for Early Saxon/Germanic tribal cavalry and Wargames Factory do cheap plastic Germanic cavalry. So I could still do Riders of Rohan on a budget.
Your Shieldwall tactic is a good idea and somewhat similar to how a real dark age shieldwall would have worked. The warriors in the front rank would have been pushing and shoving against the opposing shieldwall (close enough to smell their breath
), and wouldn't have had much space to draw and wield weapons such as swords or axes. So they used
Seaxes, a type of shortsword or long dagger, using it to stab over, under and around the enemy's shields (perhaps in a similar fashion to how a Roman Legionary would have wielded his Gladius). Meanwhile the people in the 2nd ranks etc would be shoving forwards, pressing against the men in the front rank, and throwing or jabbing with spears and making overhead chops with axes and swords whenever possible.
In game, this would work out with you using the front ranks to Shield, to maintain the line, whilst your men in the rear ranks do the killing by throwing their spears when the front rank is not engaged (when they've pushed the enemy back enough to give enough space to wield your weapons).
Oh and btw, I don't claim to have any special knowledge of how dark age combat and shieldwalls would have worked in practice, I've just been reading a lot of novels and history books on that period lately.
(Bernard Cornwell and Osprey books mainly).