Leveling and downranked spells

Is it worth using downranked spells for leveling? some times I run completely out of mana when trying to kill level 28-29 mobs(I'm level 25)
Lindow wrote:I would add rank one fireball for rogues (unless you're fire and you have Ignite) and rank one blizzard + arcane explosion, to break stealth.
But I remember blizzard normalized the mana cost of lower ranks or something at some point, so I am not sure this actually saves any mana.