After learning about the Shadeshifters, the benifit that Weiss wanted the most by destroying them was not the money that this organisation had accumulated but actually the slaves themselves.
Other than the money, one another vital thing that Weiss's Souran territory lacked was people. The population of the territory was extremely low and most of the people were regular farmers or hunters.
But among the slaves, a decent amount of them had knowledge about various different jobs like carpenter, seamstress and such.
These people would be a very valuable asset to the Souran territory that was way more important that a little bit of money.
That was why Weiss wanted to free these slaves and turn them into the citizen of her territory. According to Ganz, there were hundreds of slaves and that number would definitely give the Souran territory a much needed boost.
