Maybe the past wasn't always better, but go tell that to a person wrapped up in the spell of nostalgia. A nostalgic voice is all about romantic, wistful longing for times gone by..
Longing for "the way things used to be" is as human as breathing. While sometimes we view the past through rose-tinted glasses, a nostalgic voice goes all the way in making you believe that we're missing out. Whether it's the summer of love, simpler times, or a great relationship that's long gone, nostalgic characters always seem to be gazing longingly out of a window with a melancholy tinge in their eyes. They're so commited to their daydreaming that, before long, they'll have us sighing right along with them as well.
Sometimes a nostalgic voice is a great idea if you're bringing back a product by popular demand. Others, it's a great choice for when a character is snapped out of their reverie and shown that things can be great in the present as well and there's no need to look back constantly. Nostalgia can be a great selling point if you need to connect with simpler times when things used to be hand-crafted and made with love. In fiction, nostalgic characters tend to have suffered some great, irreplaceable loss that has them locked in a state of regret or longing that they're unable to break from.
Nostalgic voices tend to have a slow cadence, with a tone that borders on sadness. Sighs and slight exhalations are very common, as is a slightly otherwordly quality that indicates they're stuck in remembrance.