SQL Server instance running out of worker threads
Increasing MWT can lead to increased SOS_SCHEDULER_YIELD waits. Not the end of the world, but think of it like adding a buncha kids to a teacher's class. All of a sudden, it's gonna be harder for each kid to get attention. 

When a process exhausts its 4ms quantum, there will potentially be more threads ahead of it waiting to get on the CPU. It's really difficult to say if performance will be worse with that trade off.

You could try increasing MWT a incrementally. 

This is how SQL Server manages it:



Notice how doubling core counts doesn't double MWT, and you get the same number with 1 core as you do with 4 cores? 

It's like a sign, or something.

The equation is: 512 + ((logical CPUs - 4) * 16), which means at 10 cores you'd have 608 threads, and at 12 cores you'd have 640 threads. 

Those are reasonably safe increments to try, but I wouldn't go over that without a support call with Microsoft.

Hope this helps!