While I don't have an SS, I have a 14 Caprice and it shares ALOT with the SS. I got my car with 12,000 miles on it. I am at 85,000 right now The SS has the 6.2 the Caprice has 6.0. Both could be had with the 6L80E which is pretty solid in the cars. Still if you can find one, a manual SS would be nice. The 14 and up Caprice have the same suspension components as the 14 SS. Solid design, but the strut mounts suck. Drivetrain is solid. One issue both cars have is the motor mounts are so so and the bushings for the rear diff could be better. The 14 cars both SS and Caprice had a recall on the electric power steering rack where they end up replacing it with an updated one.
I have put some SS components on my dash to include the SS gauge cluster which has some nice features like lap time, oil temp, oil pressure and various other things I never use. They are solid cars, mechanical parts are easy to get. I know guys don't have much problem getting parts for the Caprice (again Holden based) but like the SS I can see 5-10 years down the line it being an issue.
It has been a solid car that I did a cam swap on to get rid of the DOD/AFM. I have done the strut mounts when I changed the springs to ones I installed from a wrecked Chevy SS. The Chevy SS is just a better version of the Caprice here in the states. I have loved my Holden built GM. It has been my favorite GM to own. I know a lot of Caprice owners also have SSs and they like both of them about the same and have said both have been solid.