On another point, using positions or locations that were not notified in some way was normally limited to locally based aircraft with voices that I recognised (usually instructors) and who I could have confidence would know where I was talking about.
But this is exactly the problem! If you arrive at an unfamiliar airport, look at your charts & GPS and hear other traffic reporting some - to you - unknown VRPs, what do you think that does for situational awareness? It goes out the window, that's what it does. I've had that happen to me several times and it's not a great feeling knowing there's traffic in the vicinity but having no idea whatsoever as to where that traffic might be. Making a radio call doesn't help much either in such a scenario, unless ATC and/or the other traffic can clearly define where they are (or ATC calls 'traffic not a factor', knowing there's no conflict).
To confuse matters a bit further, in some countries (Spain being a prime example here), the locals use a different name for published VRPs than the one on the charts. Great for SA - not.