I see your points to some extent and they would have been something for me to consider, but I know that in many cases return calls are made by WCO's to get additional info and thank the caller.
This may just be me, but when I call an agency on the phone and leave a message, if I don't request a return call and I feel that I have left detailed enough information that the agency does not need to contact me, then I don't expect to receive a return call. In my life, that's pretty much the function of voice mail. And for those of you who have cell phones at home or work (neither for me), then isn't that why you text? What I do expect is that if appropriate they will take some form of action or add the info provided to their knowledge base for future reference. I don't make the assumption that nothing is being done if I don't hear about it; quite the contrary, I assume that they are doing their jobs. If I have concerns, I follow up.
In my case, when I received a very occasional voice message about a pollution case, I forwarded the info to law enforcement, or if unavailable, then to DEP, as field actions based on pollution reports from the public were not a general part of my duties. My concentration was solely on getting the proper info to an "action person" as quickly as possible. My way of going the extra mile was to investigate to the limited extent possible and provide quality observational and locational info to WCO's on the numerous cases that I would find when I was on my own time (not working).
On the other hand, when on the job I was pretty much the contact person for all snakehead info from around the state and I acknowledged nearly every report for years, particularly since most came from the SE, but on occasion referred a report to an AFM in another region for follow-up when the report originated in that region.