Lifetime updates aside, just updating from X2 is probably worth it. Check out the
Rolling Updates page just to see what's been added since 2015, on top of what was already added in X3.
Granted, you say you're a more casual user and I noticed that you're still running Windows 7. You would likely have been better off if you'd upgraded to Windows 10 while it was still free, but that's life. My only caveat is that if what you have works well and you don't need anything more, then "freeze" your system and carry on. But if you plan to move forward with the times in the years ahead, I'd recommend Windows 10 and lifetime updates. With both of those, you're covered for updates as long as your computer can handle them.