Kory, those are good looking flies! I'm sure that estaz body helps with reducing that plop. I've yet to catch a Redfish on a fly, don't get to chase them too often. They got up into the Chesapeake & tribs this past year, a lot of puppies but I never got the opportunity. Perhaps someday!
I've used rattles in flies or many years for tidal bass, Flounders & Striped Bass and the waters I fish are quite shallow, and often stained. As you stated, if the clarity is 3', it's real good. I've caught Seatrout in similar waters, as well as Black Drum. I feel the rattles help sometimes.
Good info on the buoyancy. Many of the rattle flies I tie are tied with bucktail or other hair. I like fox & coyote tail hair, which is not buoyant. Also use some Polar fiber. Some are tied much more sparse than others, and the weighting is varied, which is not a bad idea anyway. Also, I rarely use glass rattles any more, have come to prefer the big plastic rattles, as they sound louder to me. I stick them in mylar tubing and/or EZ body type materials as a body & always coat them with epoxy. IMO, when I've wrapped soft materials around a rattle it muffles the sound. Epoxy seems to enhance the sound.
I'm not sure what I've added here is any help to Marco, but this is all interesting to me too. I've got a trip planned this year to the SC coast. Perhaps this time I'll find a Redfish!