Archaic word choice—as I have used “lo!” in a poem yesterday—similarly, at its best, serves as an attempt to polish some rust off of the antiquated lexicon: clearly not successful in all cases, yet, again in a reading society, allowing old vocabularies and formulations to slide into disuse but cuts contemporary readers off from their past. Reactivating them, at least in theory, contributes toward their potent rehabilitation, however unlikely. (I have never been happy with the “thou” usage, but, as a reviewer of my Sonnets once pointed out, it feels unseemly to address the Lord God of Hosts as “Hey you” even while traditional hymnals remain current.)
Spenser is much criticized for dredging up then archaic words (his rhyme schemes of choice practically necessitate it), whereas Shakespeare typically endorsed new coinage and contemporary slang. We prefer Shakespeare—as a rule (meaning not the royal “we” but normative social values)—however there is no justification to insist a writer today must avoid the Spenserian praxis. We do not all write in order to say, “I think I shall be among the English Poets after my death.” Rather, each poet may well be charged with a specific task—like a cat’s secret “name that no human research can discover” (per Eliot)—that only he himself can determine and designate. We do not all try to be Keats.