TLDR Version: Including "before" in such cases is fine, but rarely necessary.
In thinking about your question, I found myself pondering again on "Grice's Maxims of Communication".
These maxims are intended to encapsulate the tacit "rules" of coorperative communication. Not only are we supposed to follow these principles when we speak or write, we are supposed to assume that others are following them too, which guides our interpretation of what they are saying.
Here's your example sentence:
"More than ever, marketers require data ... to better understand their customers."
Meanwhile, Grice's maxims may be summarised as:
Maxim of Quality: Only say truthful things.
Maxim of Quantity: Say all that is required, but not more than is required.
Maxim of Relation: Be relevant.
Maxim of Manner: Be clear.
At least the first and second are relevant in this case.
If a word isn't necessary in order to get our point across, then according to the Maxim of Quantity, it would be sensible to omit it unless doing so leads us into conflict with the other maxims (most obviously by making things ambigous so running into the Maxim of Manner). So if we can omit the word "before" we almost certainly should.
But cutting in the other direction, as a matter of logic, "More than ever" really means "Now more than ever" and "ever" means "all times" and "all times" includes "now" so we may, as a matter of mere logic, interpret the original clause as either equivalent to or as including each of the following:
- "More than ever ..."
- "Now more than ever ..."
- "Now more than at all times ..."
- "Now more than at all times including now ..."
- "Now more than now ..."
Doubtless in reading that set of clauses, you found either the move from 2 to 3 or from 3 to 4 rather jarring.
But if you are persuaded by the logical connections, you'll see that since 5 is clearly nonsense, and would seem to be included by 1, 1 is also, strictly speaking, nonsense. And if you speak nonsense, then you're flouting Grice's Maxim of Quality. So we ought to expand the clause to:
- "More than ever before ..."
right? I certainly see no problem with that. And there may be odd cases where it is advisable. But actually, suppose we do omit the "before" ...
Then what will our audience think? Well, they need to assume the writer/speaker is at least trying to follow the maxims, and isn't likely to wanting commit themselves to the version beginning with 5. So as their audience for such a sentence, we'd be a very uncharitable reader/listener if we didn't assume they meant to be contrasting the present with past times rather than with all times.
And since we can generally rely on our listeners to be sympathetic listeners, we can in fact omit the word "before" entirely. It become acceptable to omit it simply because in order to understand us at all, the audience has to suppose we mean to assume it.
Now, a note of caution. Technically, to avoid being nonsense the we only need to avoid contrasting "now" with "now". There may be odd cases where "more than ever" might actually be used to mean any of the following:
- "more than ever before"
- "more than ever again"
- "more than ever before or ever again"
And in such cases, if there are any, in order to be clear (and follow the Maxim of Manner) we must make sure that we do include the extra word to avoid being misinterpreted.