The problem with healing potions is that they don't scale well at all as your level increases. As your level increases, your maximum health increases automatically, and healing potions get less and less effective. After level 10-12, healing potions are just not worthwhile anymore because enemies do more damage than healing potions can fix. It becomes a waste of AP.
I think that buffs in general - even ones from spells - should have longer durations, because the AP costs for some tend to be steep enough that when cast on yourself, you effectively lose any productive actions for the rest of your turn.
