Hey, first I wanted to say thanks for the kind words.
The Elysium Edition ($20) is for people who really want to support the game financially; it contains two side stories: Vespera, the MC's first girlfriend, and his adventures at a strip club, called Club Aegis.
So far, the Elysium Edition adds 6 characters, and there are a total of two scenes. These numbers will be expanded upon with each update to Stranded in Space.
However, the Elysium Edition content is not integral to the main plot of Stranded in Space. It is optional, meant for people who really want to support the game and want some extra content.
As far as your question goes: The next update (Days 12-13) have two more Elysium Edition scenes. This will also cost $20, but buying it will also give the current version of the game (Days 9-11) Elysium content.
So in other words, a one time purchase of any Elysium Edition will unlock all Elysium Edition content, up to that point.