When I first read the headline I tought this is not useful. Especially because I've many undolved mysteries in my area...
After some investigation I find the idea extremly usefull because the great functionality of PGCs map can be further improved.
Following functions are needed in my view:
- show corrected coordinates (e.g. solved puzzles) => should work as you wrote
- show all stations of caches (also selectable show physical/virtual can be useful to not lead multi-cachers to virtual stations with questions on signs/hotspots of other caches)
- import function of own waypoints (planned powertrails / new caches)
Should technically easy be implementable (import gpx and show as extra layer).
OK - when this works, the next feature should be a "click on the map and add this Point to a new waypoint-list that can be exported as gpx" ;-)