Possibly, are you thinking too hard about this? :) Why would you ever want to write "a" if it were simply grammatically correct but difficult to speak? The lack of consonants between "più" and "alcuna" in the phrase begs for a consonant somewhere between the vowels. Your impression that "d" was for purposes of pronunciation seems absolutely spot on to me :)
It isn't grammatically incorrect and you're right that "ad" is just like "ed", entirely optional; it's just very common before words starting with "a" because of pronunciation issues, as you said.