I'd like to get a measure of how much quieter before vs after dynamat using a series of scenarios (driving, idling, etc).

Well, I hope that you really want to measure how much quieter after vs before dynamat...

What the heck, if you're just looking for some feel-good-factor objective measurements then an RTA should give you some. My point was that trying to use an RTA to locate parts of the car to damp would probably result in you chasing your tail around in circles. But it should still show differences before/after.

Of course, you'll need a calibrated microphone to do that anyway, which a cheap SPL meter from Ratshack will provide. So taking simple SPL measurements is always an option too.

Something else to consider is that 'driving' noise is basically due to 3 elements. Engine, wind and tires. Aside from the dynamat, you'll also want to consider door/window seals (old seals are less flexible, and therefore worse than new), and potentially different tires. Unless you're doing a lot of track time then trading 3% of traction for a 20% reduction in tire noise has to be considered. ('stang forums and reviews at tirerack.com could help here)