The Idea in Brief
The plural form (maḥămaddîm) is not literary, but is to be understood in the literal sense. That is, Jewish sages over the centuries did not understand the plural form here in any literary (or abstract) sense, but in the most literal way. In this regard, the plural suffix was in reference to sweet words (plural) that emanate from the mouth of the beloved.
For example, the Targum of the Song of Songs appeared between the 1st and 4th Century, and the provides the following translation from Hebrew into Aramaic.
Suggested translation: The words upon the palate of sweetness are like honey, and all his commands are pleasing to his wise counsellors than gold [or silver]. This is the splendor of God, my beloved, and this is the power of the strength of my Lord, my beloved, O prophets who prophesy in Jerusalem.
Rabbi Shlomo Yitzchaki (Rashi) lived in the 11th Century, and he also notes that the plural form of sweetness was the actual reference to the words in the mouth of the beloved. The following comes from the relevant cite reference on the www.chabad.org website.
 His palate is sweet: His words are pleasant, e.g. (Lev. 19:28): “And you shall not make a wound in your flesh for one who has died… I am the Lord,” faithful to pay reward. Is there a palate sweeter than this? Do not wound yourselves, and you will receive reward. (Ezek. 33:19): “And when a wicked man repents of his wickedness and performs justice and righteousness, he shall live because of them.” Iniquities are accounted to him as merits. Is there a palate sweeter than this? (emphasis added)
Early Jewish Halakic (legal) midrash echos of the same. The Mekhilta de-Rabbi Shimon bar Yohai, which are midrash ascribed to Rabbi Simeon bar Yochai who was one 2nd-century tannaitic sage in ancient Israel after the destruction of the Second Temple. The midrash notes the following:
The following translation comes from Nelson (2006).
Rather, “His mouth is delicious, etc.” (Song 5:16). And Scripture says, “...to the sound that comes out of His mouth” (Job 37:2).
The midrash here makes the explicit connection between words and the deliciousness of those words as the sound [of the words] coming from the same mouth.
In summary, rabbinic scholars over the centuries (who were intimate with Jewish oral tradition and the Jewish understanding of the Hebrew Scriptures) had understood the plural form (maḥămaddîm) as in literal reference to sweet words, and not to something abstract.
Nelson, W. David (2006). Mekhilta de-Rabbi Shimon bar Yohai. Philadelphia: Jewish Publication Society, 130.