I'd have to say the Priceless Portrait was indeed the most out of place artifact on the show. The producers probably were thinking "This is going to be our last episode of this season and we haven't used in the Laser Light Room for any artifacts, so let's shove this one there.". Which is surprising considering the Laser Light Room appeared in more than half of Season 2. The Priceless Portrait would've made more sense in the King's Storeroom due to the association with pottery and art.
The Stone Head is one that they messed up big time. It would've made much more sense to put it in Medusa's Lair, considering the legend revolves around Medusa. I really wonder why they didn't do that considering how obvious the connection.
To me, the Missing Portrait makes sense to a certain extent in the Chamber of the Sacred Markers. I mean a portrait could be considered a "marker" of some sort. The King's Storeroom does sound like a more logical place either way.
The Leopard-Skin Cloak is real strange one like the Lucky Pillow as they seem to have no relevance to the room at all. Some of the artifacts you can make a connection to their room through their legend (like the Lily-Crested Crown and Quicksand Bog), but these two you can't. I agree with this one.
I honestly don't know where I would've put the Bent Shaving Pan at though. I can't think of a S3 room that would fit this artifact properly.
One more I want to add is the Sacred Ring being in the Dark Forest. Wow, this one should've been easily put in the King's Storeroom rather than the Dark Forest. It doesn't even make sense in the Dark Forest and it looks silly having the Dark Forest tree where it.

Later, I am going to put some of these suggestions into the first post and give you guys credit.
