I think that most of the information that a new geo-cacher needs to know about trackables is already out the be found. Unfortunately it's not well placed. Most of the information seems to come when you attempt to log a trackable item or if you're the type that is serious about reading all of the documention before you begin a new activity (and I know very few people that are like this.)
I think the question is more of "Where can we place this information to ensure that people retrieve it." I'd suggest a warning banner (or banners) along with the cache information for any cache that contains a trackable with the minimal explanation that trackable items aren't swag and they're owned by another cacher and then link the individual to more information.
I'd even suggest that a rather inexpensive coin/tag be provided to each new member of the site with the information about how this aspect of the game is to be played. It won't stop everyone as there will always be malicious people that think of their enjoyment only. Provide some emotional and preferably true stories about the great joy that members have derived from sending trackables into the wild to get at new members emotionally and encourage their participation in this aspect of the game.
Stop comparing geocaching to a global treasure hunt! I find that this endagners geocoins especially as they are a match (in most cases) for the image of treasure conjured by the mind.
This discussion, the number of items that are being sold (both in-house and externally) are a testament to the fact that trackables are a growing and important aspect of the game. The particulars of this part of the game can no longer be buried in the depths of the site where they're likely to never be seen.
Having said all of that, the problem will be one slow to go away. There are too many people already that seem uninformed about the true specifics of trackables. They're fixed on collecting treasure. As the rankers of geocachers grow and are properly educated we can hope that the demographics will change enough that the problem will become smaller and people will educate those who unwittingly took treasured trackables out of circulation to understand the game.