A quick check of players buffs when grinding shows me that potions are underused when leveling. I'm level 25 Feral Druid now and still use the minor pot's such as fortitude, lion's strength, etc, and especially elixir of wisdom. The minor's are cheap - 1s or less usually, and wisdom about 5s in the AH. The wisdom pot essentially is cost neutral, as it helps me cut down the cost of drinks.
As an example how this works, when grinding heavily mobbed areas (say 40 kills/hour area), the wisdom gives me about a 10% boost in mana (more at lower levels). I've found that I can cut out over half my down time for drinking, saving nearly the cost of the pot, At the end of a fight where I've used mana for initiating the attack, or popping to heal myself (especially if I've drawn more adds), without the 10% boost, I often stop to drink -- with the boost, I often have enough mana to initiate another fight. Another benefit I've experienced is fewer death runs. Overall, I feel the wisdom helps me speed up grind leveling by about 10%.
I'm certain other caster classes (even mages with their free water) would see similar benefits using the elixir of wisdom.
Q