I'm not necessarily the target audience for these, but I think I'd prefer a main box with a good variety of heads and melee weapons (axes, swords, clubs, etc.), and then a generic spear-and-arcery sprue, which could be re-used for most armies around the world throughout history: sure, the details would be noticeable to an expert with a magnifying glass, and sometimes bows or spears might be really distinctive for a given army, but the basic spear and shortbow really don't change vey much from culture to culture, era to era.
You could even focus army-builder sprues on heads and bodies, and include the standard, generic spear-and-archry sprues in the boxes for thoe armies where it's appropriate.
Or, in addition to selling the spear-and-archery sprue separately, you could offer set bundles: Order (say) three boxes of Egyptian infantry, get a spear-and-archery sprue for free. Just a thought....
YMMV, but for my part, I've got LOTS of spear and bow arms (and quivers and drawing-arms) in my bits box. It seems like I don't use them as often as swords and other melee weapons. I've given lots away, or trim them and use them for scenery or for small scratch-building projects (I've used bits of shortbow for horns and spikes, or for crossbow arms, etc.) It's been easy for me to accumulate more spears and bows than I need!