Is there any way to find out if the timing chain and tensioners have ever been replaced? With 130,000 on mine, I'm in the process of changing the timing and camshaft chain and tensioners (as preventative measures) If you want piece of mind, just perform the usual changes at recommended intervals. You can perform a compression test on the cylinders to see how the engine is doing internally. Other than that, keep her clean (especially if you live in the rust belt) Keep an eye on bubbles in paint as an indication of rust, and get to it before it takes off and puts an ugly hole in the body.
That's all I can really think of so far...
2006 Cobalt SS/NA