I can't help you on when the Sig was manufactured.
As for improvements, I've never seen grips that topped the factory panels. A custom set has to be built around the thumb decocker lever.
As for improvements, a trigger job by a reliable smith could help. Most Sigs smooth out with use, however. I like to put a pair of night sights on Sigs that weren't so equipped at the factory. The standard finish wears quite quickly. I'd probably look for a more durable finish such as one by Robar, Accurate Plating and Weaponry, etc.
One doesn't have to tinker much with a Sig. You can buy two from what you would save not sending the first to a smith.