Well i finished up the strakes, got them mounted and put a layer of flat-black on the whole thing. I also replaced the SS exhaust heat shield on the diffuser with a larger one that can keep all the exhaust off the aluminum as well as lift it up a little higher to disrupt underbody airflow less.
Just after I finished installing the strakes and painting (still wet, hence the gloss):
I'm going to call the underbody V2 project done at this point. I might tweak it a little here or there later on, but that'll just be a continuation of I-cant-leave-anything-alone. On to the next thing!