Went back through my game, and yes, I had every single item. I saw in another thread that possibly the money-money 1g drops counted. So, I started over and played all the way through the game again. This time I did 2 things different. 1. I picked up the light lens in the cages after being captured at grand staff and 2. I picked up all of the 1g drops from money-money. When I got to the end, and picked up the last item my achievement finally popped. Seems that these two items are likely very important, but just failed to get into the guide.
How to get the light lens is simple when you know how. It is timed though, so you'll need to be quick about it. *SPOILERS*!! When you are all captured and in seperate cages General Kakanus will come and speak to you, and then you have control of Kaim. Do the following to get your light lens, and hopefully put you one item closer to Treasure Trove.
1. Ram the door with Kaim
2. Switch to Jansen
3. Don't ram the door. Investigate the SW corner to find a rat with "something" in it's mouth.
4. Kick it
5. Switch to Seth
6. Don't ram the door. Investigate the same spot you found the rat in Jansen's cage, and kick it.
7. Switch to Kaim
8. Now you can get the Light Lens in the same place as the rat. If I remember correctly it is a glowing thing on the ground.
Good luck, and I do hope that this helps anyone going for this achievement.