[Radek]

I don't think level 7 Vine spells are the best, either. More precisely, their effectiveness does not correspond to their level. In my experience, Whirling Dervish is the far weakest storm spell. As Bungleau has hinted, Vine of Life might be useful when you try to open a chest which is above your possibilities but... But at low levels when such chests do occur, you don't have the spell. At high levels, you have the spell but the are no more chests above your possibilities or your number of HP and resistances are enough high to make the spell unessential.
In the other words, acquiring level 7 Vine spells results in getting some mana points for Vine magic, that's all.