I don't think that either smell nor "non-water compounds" are reasons to regulate e-cigarettes tighter than we regulate perfumes, colognes, or spray deodorants.
Similar regulation for all four seems reasonable to me.
Those things don't tend to protrude more than a few inches, maximum, from a person's body, and there's an established culture whereby people will be reprimanded if they do.
Quite a few perfumes give me a migraine with even fairly limited exposure. By the time I notice the smell enough to run away, it's usually too late. If someone is wearing axe body spray I have to immediately leave the room.
This is the reason I stopped going to malls. The olfactory assault emanating from some of those stores is quite unpleasant and will give me migraines. Applies to the weekend bar scene, too, but I was never wont to hang around drunk people anyway.
Similar regulation for all four seems reasonable to me.