No, I did not have to change the power or transducer cables, they were the same. I asked that same question to Simrad at least 4 times, lol. My unit is flush mounted into my center console, so I had to cut the opening a little wider, as the NSS9 is a wider unit due to the controls on the right side. Power and transducer cables remained in the boat. They shipped me a brand new NSS Evo3, without transducer, just the unit. But it had all the hardware and mounting supplies in the box, so I rigged up the new power wire that came in the box so we could use it to power up my buddies GO7 in the truck on road trips. If you're not flush mounted, Im almost certain you'd need to use the new mount because the NSS is a little wider.
The resolution on the NSS Evo3 is much better than the GO9, much sharper when zooming in tight. The NSS Evo3 also has a layer over the glass which allows the screen to appear just as bright in direct sunlight when wearing polarized glasses, which is great. I often found myself lifting my glasses to see the screen on the GO. I was really unsure if I would like the hard knobs on the side, because I really liked the smooth, clean look of the GO9. But after having the NSS Evo3, I absolutely love the hard buttons, and rarely if ever touch the screen for anything. Zooming in and out with the knob is lightning fast. NSS has dual processors, its very fast.
Hope that helps.