Just to make sure you have all of the information you need...
Level 30 BSpear with 3 synergies maxed does 1782-1862 points of magic damage.
Level 30 BSpirit with 3 synergies maxed does 2668-2866 points of magic damage.
I cannot find any point where an equivalent level of bone spear will get near the damage of bone spirit to a single opponent. With White on a good wand, though, it is possible to get a much higher level Spear than Spirit, to try to get them closer together.
Again, since spear pierces, you can get more total damage with spear than spirit.
You should do fine against bosses with Bone Spear until you get up to high spirit damage. It will take a little longer, but you'll still be okay.
Porius
Level 30 BSpear with 3 synergies maxed does 1782-1862 points of magic damage.
Level 30 BSpirit with 3 synergies maxed does 2668-2866 points of magic damage.
I cannot find any point where an equivalent level of bone spear will get near the damage of bone spirit to a single opponent. With White on a good wand, though, it is possible to get a much higher level Spear than Spirit, to try to get them closer together.
Again, since spear pierces, you can get more total damage with spear than spirit.
You should do fine against bosses with Bone Spear until you get up to high spirit damage. It will take a little longer, but you'll still be okay.
Porius