It ain't easy to incorrectly plug the PSU's power cable in unless you are a gorilla, so the possibility that you were pushing volts into somewhere it shouldn't be and blowing up IC's and components is unlikely. Also the 950 has onboard video so you can pull all your cards out and you'll still have an onboard source. In fact, with all NuBus and PDS cards removed and just one bank filled with ram you should get a chime.

While the machine no longer chiming isn't a good start it could of been something as easy as a tantalum capacitor shorted out and yes, I have seen them short out between immediate recent power cycles with absolutely no warning (and this could of been what blew on the NuVista because I can't see ANY damage to that board).  I'd recommend trying to run the machine completely stripped to the basics (no hard dirve or floppy drives attached either) and see what happens. Also pull the machine apart if you prefer and see if you've accidentially left a screw somewhere that rolled under the logic board because yeah, that will kill it.

Also, don't dump the cards just yet. Avid boards are rather nice if you're into old fashioned capture rigs, especially if they have the compression board. If you do plan to dump them regardless, talk to me because I'm setup to better verify if indeed the boards are dead or not (plus I have spare cables and the likes). Heck, if you want to send the whole logic board I can test to see if it is still working as I got all the tools needed to better analyze if things like the clock and the Bus controllers are still doing anything.