foliar sprays do more for human psyches than actually aid the plant in any way... if you need foliar sprays tosupplement fertilization, that means your fertilization is off. it's a tool for specific problems, yes, but to use in general invites more risk than benefits.
now, something like a neem application to preemptively avoid a problem is a different thing. You shouldn't need vitamins or other stuff in a general foliar spray... it should get all it needs at far as nutrients from the roots, preferably.