I brought a board breaker to France and got several pink diamonds from using it. I gave them the heart cut while still in France; when my Sim returned home to Sunset Valley the heart cut pink diamonds were worth the same as they had been before they were cut.
Then she got 3 Tiberium from the board breaker in Sunset Valley. As they hadn't yet turned to crystals I left them in her inventory when she went to Egypt. As soon as she got there they made her sick so I put the Tiberium on the ground by her vacation home and after a few days they turned to crystals worth about 40.000 simoleons each. I put those back in her inventory so she could bring them back home. When she got home they were only worth around 500 simoleons each.
After a lot of tinkering with the cool transmogrifying display case and using up all my metals I had managed to make a Compendium ingot worth 26.000 simoleons. After the round trip to Egypt and back this was now worth 758 simoleons.
Akh! Akh!! Akh!!!
I am so mad I've scrapped that game and started a new one.