Rather than having Value always be a String, something like this could be better:

enum Value {
    String(String),
    Integer(i64),
    Float(f64),
}

And then the From implementations would just set an Integer or Float. This would be nice because it means that numbers (which account for a lot of possible values) never have to allocate.

Doing deref to str wouldn't be the best thing with this change. Something like as_string() -> String might be better suited.