If there was a NOTAM issued every time they are going to jump then that will help a little but seriously I liken the location to jumping out overhead Carrum. Mind you, Elwood is next to Brighton which is essentially an approach point for GAAP. Not so much am I overly concerned about the chutes as such but the aircraft dropping them, they are out to get up and down as quick as they can so you are certanily right about vertical and horizontal traffic.
Tooradin has been operating next to water for near 6 years and they haven't lost anyone to the water yet.
Do you really want parachute aircraft to be charged for VFR CTA clearances? If you kept pushing that and it happened, god help us all.