If you're happy with things and nothing is acting weird or badly, You're more or less golden, like folks are saying.

Where you might find that one day you want a newer kernel or packages (which is why you'd switch to Arch or one of its derivatives), is if you ever have very new hardware (or very old hardware that just got a driver pulled into the kernel - I own a Digidesign 002Rack that is ancient, but someone finally wrote a driver for it, and it's still a great piece of audio hardware) that only has drivers in the latest kernels.

But if you're just doing web, Office type stuff, even Steam games, you shouldn't need anything more than you have already.

I am a fan of the KDE desktop, myself, and I recommend that everyone try it out at some point. But you should be able to install it onto Mint and just choose it when you login, again, no need to change distros.