Most of the ways out of Fort Joy go right through the fort, which means easy access to the paintings. Larian might as well have placed a huge heap of 500 gold in the middle of an empty room for all the balance the paintings have.
This is not a good way to handle the game economy. Every single painting on Fort Joy should be changed to be worth exactly 0 gold, because absolutely no one on the island has any use for such paintings.
Although the paintings might not be the most logical choice, I think the game does need that 500 gold (or perhaps a bit more) that needs a little work to get otherwise there's pretty much no chance of getting your team kitted out with at least some half-decent equipment and skills before they head out into the marshes. If they do give the paintings zero value, I think they're really going to have to put
something in their place; though one could also argue that even arms and armour and their sellers are out of place in a prison area where everyone is dressed in rags. But I guess at that point I'm inclined to overlook the need for realism, in much the same way as I tend to do for things like "abridged" versions of building interiors that you usually get in video games.
