that depends on many things... 400 polys might be low for some exotic-looking spear especially if its going to be visible in detail, on the other hand, if you will need many such spears on screen at once and the spear itself wont be visible in close-up (like in some RTS game), then perhaps there is no need for those 400 polygons...
either way 400 polygons doesn't seem that much to me, but then again, it depends on what it will be used for
