I've seen some comments about what EVE and, by extension, Salts are. Wiki says that EVE is modified ADAM, but my opinion is that it's actually your character's ability to focus to project Plasmid/Vigor powers.
It's basically something carried over from System Shock 2. In System Shock 2, your magical abilities were from psychic powers. Like in Bioshock, you had a certain amount of points you could use before you could no longer use PSI abilities. To restore PSI Points, you could use PSI Hypos. To quote the System Shock wiki:
"The psi hypo contains a potent cocktail of tension relievers, dopamine inhibitors, and circulatory stimulators. The Surgeon General has warned that psi hypos can be habit-forming and dangerous to your health."
Basically, in SS2, your character's PSI points were his ability to focus when using PSI powers.
Now, let's get back to Bioshock. In Bioshock games, cigarettes increase your EVE/Salts, while drinking alcohol decreases your EVE/Salts. Think about SS2's PSI points and what they represent. Wouldn't it make sense that smoking cigarettes would increase your character's ability to focus their mental powers to use Plasmids/Vigors (remember, cigarettes relax you in real life), while drinking alcohol would decrease their ability to focus their mental powers (alcohol negatively impacts how the mind works)?
In Infinite, Salt vials have "invigorating!" on them. If Salts is actually a game representation of your character's ability to focus to use Vigors, then the "invigorating!" makes a bit of sense.
Considering that the Bioshock series is System Shock 2's spiritual successor, then some concepts from System Shock 2 popping up in Bioshock isn't unexpected at all. It makes more sense than EVE/Salts being processed ADAM or whatever. It explains why EVE Hypos and Salts vials are everywhere, as they're basically uppers drugs/mental simulants that relax your character enough for them to use their Plasmids/Vigors. That's why EVE Hypos are everywhere, though they would be hard to make from a lore point of view if they were processed ADAM. For Salts, they could be used by anyone as a mental stimulant, which explains why you see Salts vials everywhere and machines dedicated to giving you a whiff of Salts, even though not a lot of people use Vigors.
Now, I'm not expecting this on the wiki or anything because it's pure conjecture. It's just something to think about the next time you play Bioshock games.