We don't know yet. But, for instance, the Cambridge Analytica data is nearly a decade old, and we didn't know back then that it could be used to (potentially) hijack a Presidential election. It's not so much a matter of what a hacker could do with this data today, but rather in 10 or 20 years.

We've established the genetic data are valuable in the aggregate.

Also since we're talking criminals, blackmail: eg tell your employer about your predisposition to violent mental illness or reveal your kids aren't actually your spouse's.

It's probably not the juiciest target, but I could see intelligence agencies wanting it. Combine it with the OPM hack of all security clearances and you could in theory use it to find family members of spies, people in high positions who have secret children, etc etc. Imagine if you had Trump's DNA and could then search a massive database to find out if he has any kids we don't know about...

If intelligence agencies wanted DNA it seems remarkably easy for them to collect. We leave our DNA everywhere.

Sure, but it would be a massive amount of work to go collect millions of samples and sequence them. Like how researchers are using the data to solve crimes, you need a large set of data to get good results out of. In my scenario you would collect the DNA of your target (say, Trump) and then use the 23andMe data to try and dig up dirt on relatives (say, his illegitimate children).