I don't think you can change the vacuum on these cars at all. It's a mechanically driven vacuum pump. Faster it spins, more vacuum it makes. So blipping the throttle makes the pump spin faster.

It's either bad wastegates, bad solenoids (unlikely) or boost leak. I would check entire intercooler system for leaks. Try to get to the wastegate arms and see how much play they have.

I agree with this, hence my confusion as to why my vacuum levels drop when I hit the throttle. I don't have any evidence of vacuum leaks, so I should check for boost leaks as you say. That aside, I still would like to know if anyone has reference values for what my vacuum levels should look like when the vehicle is under load. Thanks.