100% of charter cities are doomed within a decade for reasons I've posted above.

A charter city becoming "more valuable" does not add to it's defense against the host state. If anything, the charter city becoming more valuable makes it MORE ATTRACTIVE to be plundered by the host state.

Think about it this way: if you were a commie tin-pot dictator and your formal political rival gave a bunch of undesirables (in your opinion) some land to make a community out of, but then suddenly those undesirables became really rich, what would you do?

You'd pillage them as much as you possibly could. That's exactly what you'd do.