Vanhoozer answers your question somewhat himself in Is There a Meaning in the Text? (at least from his perspective). He states (emphasis added and comments in brackets added by me):
It is most important to distinguish literalistic from literal
interpretation. The former [literalistic] generates an unlettered, ultimately
illiterate reading—one that is incapable of recognizing less obvious uses of language such as metaphor, satire, and so forth. By
contrast, the latter [literal] attends to what authors are doing in tending to
their words in a certain way. "Literalistic" interpretation is like a
word-for-word translation that yields verbally exact or "formally
equivalent" versions but that also runs the risk of overlooking the
main (illocutionary) point. Literal interpretation, on the other hand,
is more like a translation that strives for dynamic equivalence and
yields the literary sense. [I dislike this preceding analogy, see my comments below.] The distinction, then, is between
"empirically minded" interpreters [his literalistic], who, in their zeal for factual
correspondence, take an unimaginative, almost positivist, view of
things, and "literate-minded" readers [his literal], who are sensitive to context
and familiar with how literary texts work. Interpreters err either
when they allegorize discourse that is intended to be taken literally [i.e. an allegorical interpreter]
or when they "literalize" discourse that is intended to be taken
figuratively [i.e his literalistic interpreter].
There are two things I would qualify Vanhoozer's statement with:
First, his use of paralleling "formal" versus "dynamic" translation to his "literalistic" versus "literal" interpretation is problematic. A formal translation attempts to inject as little interpretation into the target language as possible (there is always some interpretation, simply in selecting which word in the target language best communicates what the original language had), whereas a dynamic translation is more free in trying to include an interpretation into the language of the target translation, even to the point of using a phrase that completely obscures what the original words might have been.
In contrast, both a literalistic and literal interpretation are still chiefly interpretations. The literalistic theoretically does not seek for any additional symbolism beyond the straight meaning of the words themselves—I say "theoretically," because I do not know anyone in his or her right mind who would ever argue, for example, that Christ was literally a door, that is, "a movable, usually solid, barrier for opening and closing an entranceway, cupboard, cabinet, or the like, commonly turning on hinges or sliding in grooves". A literal interpretation more readily allows for other layers of symbolism to a statement, which leads to:
Second, my own understanding of a literal interpretation (a.k.a. historical-grammatical interpretation) of Scripture is that:
- It considers the aspects of the text itself (grammar, syntax, genre, literary context, etc.). NOTE: a true literalistic (rather than literal) interpretation would ignore genre and possibly aspects of literary context.
- It considers the historical context of the human author.
- It considers the larger literary context of Scripture in total and the eternal historical context that the divine Author exists within (this point is only true if one deems the Scripture to be both human and divine product, i.e. inspired, which insures the unity across the various human authors and recognizes a divine perspective that may exceed, yet include, the human perspective).
- It considers that communication is intended for exactly that, to communicate what the author was intending to the audience he/He was intending it to (which eliminates arbitrary figurative speculations [i.e. undefined allegory] from the realm of possibility). This upholds the importance of authorial intent (both human and divine).
- That what is stated is factually correct, either from a literal or figurative sense (or both, depending on one's exact form of a literal hermeneutic—I'm thinking of typology here, where something has both meanings intended). This flows from both 3 and 4, God will not factually be in error (or lie), and communication does not communicate if it is not referring to some actuality (though it may refer to that actuality symbolically).
- That if what is stated makes sense literally from the literary and historical context and reality itself (as known, which is of course part of the historical context), that the literal sense ought not to be ignored in favor of a purely figurative sense (i.e. that the message of the Bible is not simply a bunch of symbols that needs decoding to understand, particularly decoding using some mystical knowledge that cannot be derived from normal experience, history, and the text itself as the authors have defined the symbols).
It is #6 that most distinguishes a literal interpretation from others. A truly literalistic hermeneutic would ignore aspects of reality and authorial context/intent to maintain (whereas allegorical does likewise, but ignoring different aspects... this is essentially the last point of Vanhoozer in the quote I gave).
Honestly, I do not know anyone that truly holds to a pure "literalistic" hermeneutic as described, but there are those who tend more toward that than not. More common is the accusation from allegorists that literal interpreters are not being literalistic in all their interpretation (which shows ignorance in understanding what a literal hermeneutic is). So in short, your final question is correct if converted into a statement:
[Referring to literalistic is] simply an attempt to differentiate what a "literal" reading is
Disclaimer: I consider myself to hold to a literal [not literalistic] hermeneutic.