|Sarcastic Jazz Hands|
I look at it this way with the Elixir:
While it is in your hand, it is essentially in your pack/satchel/belt ready to be drank at any moment. Once it is displayed (drank) the power is in effect. It will have a finite duration, but you move down the card applying powers in order. Example, over the course of the turn from separate sources, you take 1 acid, 1 fire, and then 2 cold. The acid and the fire damage are each reduced with the card remaining in play. When the cold damage is taken, the elixir is banished.
For Enhance, all spells are now banish at the end of turn they are used I do believe, with the options to recharge if you are proficient. This again stems from spells duration. Items/elixirs often have a longer duration than corresponding spells.