Do you think there is a specific reason Hawthorne draws attention to himself in the introduction or did he just happen to frame it that way?
"Rappaccini's Daughter" was originally titled "Writings of Aubépine: Rappaccini's Daughter." Aubépine is French for the hawthorn plant. So, Aubépine is Hawthorne. And the answer to your question is yes, he did this for a specific reason. Hawthorne, the author, not the plant, found himself in an odd position between the lofty Transcendentalist writers and writers who wrote for a more common, popular audience. Although Hawthorne was calling attention to the difficulty of the fact that his writing is not viewed as essentially scholarly nor essentially pop culture, he tries to use this labeling of his work to his advantage. Towards the end of the introduction, he writes,
“We will only add to this very cursory notice, that M. de l'Aubépine's productions, if the reader chance to take them in precisely the proper point of view, may amuse a leisure hour as well as those of a brighter man; if otherwise, they can hardly fail to look excessively like nonsense.”
Hawthorne is using this introduction to say that his writing can be read for enlightenment and pleasure. This is also clever because the pun on Aubépine with the hawthorn plant is an allusion with the role of plants in the upcoming story. In the story, plants function as both a poison and a cure, paralleling the duality of Hawthorne's writing as being both scholarly and entertaining. A plant that is both poison and cure reflects Hawthorne's position as a writer between the academic and popular circles. This can work to Hawthorne's benefit (being read by both academics and the multitudes) or to his detriment (being read by neither). Hawthorne frequently wrote about the dualities, certainly with respect to human nature.