The 1837 edition removed the pronoun it before is, with the result that the original subordinate conjunction that is reinterpreted as the subject pronoun that (“and say : that is of no worth”). The 1981 LDS edition initially followed the preceding LDS textual tradition in omitting the it, but in later printings of that edition (beginning sometime in 1983) the it was restored. The 1837 change was probably a typo since it is uncharacteristic of Joseph Smith’s editing for that edition. Nor was this change marked by Joseph in the printer’s manuscript. In fact, the it was restored in the 1840 edition, which was also edited by him. The earliest textual sources (𝓟 and the 1830 edition) have the correct reading (“and say that it is of no worth”).
Summary: Retain the reading with it in “it is of no worth”, in accord with the earliest textual sources for 2 Nephi 28:16.