While the VA decision might end up being a double edged sword for Dems if this standing issue is used against them in other cases, the reaffirmation of dual sovereignty will help the Dems and hurt Trump and his associates personally.
NYS can prosecute Manafort for the same crimes that the Feds prosecuted him on. A pardon has no value for him. Manhattan DA is already prosecuting Manafort for additional crimes. That might actually get him to cough up evidence that he denied Mueller in exchange for a shorter sentence. An impeachment proceeding might change Manafort’s political calculus as he might think Trump too weak and undependable to stay in jail for. Problem for Manafort is that his credibility is shot but perhaps he has stashes and docs he can offer.
This will also factor into the Trump family’s thinking on tax and financial fraud claims. If Dems ever get the political will to open a formal impeachment inquiry, you could see a flood of action in the courts as it becomes open season on anything Trump.