If you have any mages with death and fire, they can make flaming skulls which provide +1 to fire magic. Otherwise the fire helmet booster needs 4F, or you could use an elemental staff that needs either 4E4A or 4F4W... So you generally kinda need 4F in order to get to 4F.
Also, there's a new conjuration spell (I think it's Conj. 6?) that lets you summon a commander that has innate 3F, which then goes up to 4F with any kind of booster, or potentially empowerment.
There are a couple other booster items, but they're both demanding pathwise and exorbitantly expensive.
On a completely different note, I've just been doing some dicking around with a test game... Turns out stacking two eyes of aiming doesn't give you anything good even on a blind unit, as the +8 bonus only applies from the first eye. The second one just eats a misc slot and does nothing.
However, one eye of aiming will give an olm sage (EA Agartha cap-only commander) 20 precision before any other modifiers... Which is nothing to sneeze at, considering Agartha can also get the forge lord pretender and potentially make eyes of aiming for 1 gem each.
Another thing I found out is perhaps even more interesting... You know how the spell description for flaming arrows mentions how it doesn't affect magic weapons? That generally means that any bows o' botulf or whatnot you've got your commanders toting around won't get the bonus.
However, a fire bless DOES affect magic weapons. If you've got a sacred commander and a fire bless, you can give them a bow of war and turn it into a bow of FLAMING war; which is pretty nifty, all things considered.
And thanks for pointing me at the Wind Guide spell. Seriously, how do they (the game's creators) expect someone to keep track of all this stuff? There's like three hundred spells in there! :\
I think a lot of people tend to think of it as "okay, there are some 300+ spells, of which 20 are worth remembering". It's more just a matter of figuring out which ones are noteworthy (wind guide, flaming arrows), and which ones aren't (bog beasts, ghost ship armada).