There's a six-month free update window after purchase. After that, a fee is charged. Many updates are maintenance releases - fixes and perhaps an added feature.
But there's no mandate to update, and as you say, your version is good for 'life.' So, if it works well for you, consider sticking with it.
You can check out the latest, unlicensed, to see if it offers anything interesting. That trial should be full featured for a short time. Save your purchased installer.
If you have lost it, look here. Ignore any virus warnings.