As far as the ice wand curing more, I'd just chalk it up the random numbers because the difference in the average wasn't anything significant.

Crowned Cakes only affect MP and Magic Potency. Requiring different stats for the food, in the cake's case, Ice Affinity and INT, changed the bonuses they gave. For example, normally the cakes would give you X amount of MP and Magic Potency, but getting closer to the target numbers would increase the bonus, with Divine being the best and I think giving you near double the plain bonus. Food bonuses are based entirely on what category of food you eat, with sweets being dat mined and tested as giving MP and Attack Magic Potency. There is no difference between individual "sweets" foods except that they had different target stats and therefore you were meant to upgrade as you leveled up.

For elemental attributes: the numbers on your character status screen is now resistance only. From my experience, Elemental Potency is simply "Attack Magic Potency" but only applicable to a specific element. Elemental Potency bonuses come in more concentrated values than straight Attack Magic Potency, and now that mages have specific elements that they specialize in, Elemental potency is worth looking into.