Well it depends.
Sometimes less is more. Other times more is more.
A long time ago when I started retouching, I'd often take things too far. Whether it was the overcooked colors or the plasticizing skin treatment, I'd often wind up too far in one direction or another.
Fast forward about 4 years.
I find myself wanting to do less. I still look through many of the adjustment layers I typically use. But I don't apply the same amount of "force".
Amy Dresser said (in a RetouchPro.com broadcast), that she didn't like being "heavy-handed" in her retouching. I find this to have been an underlying theme with my work over the last couple years.
That means lots of blend, opacity, feather, flow, adjustments that are much lower than you'd think. Like my brush/heal/stamp flow is set to 1% (opacity set to 100%).
Just like you like your milk. Personally however, I prefer whole milk. 1%/2% tastes watered down. Even worse than diet soda, which I despise.
But the real question (one that I get often) is, "How do I know if I've gone far enough/too far?"
Now that's the million-dollar question.
But to that question I'd ask, "What would be artistic value of retouching if someone could tell you exactly how far to go?"
Let me rephrase. Are you looking to create art or are you looking to reproduce industry standards? Because it really depends on what your goals are. For example, if you're a beauty retoucher looking to book beauty retouching work, you should flip through the trade magazines and make sure your images look exactly like the ones in there. And don't get me wrong. There's no shame in adhering to the current standards of retouching. It makes perfect sense if you are trying to book that kind of work.
But if you're trying to find your own voice and create your own style/brand then I'd suggest you first learn the basics and then branch off and try some new tricks. Go on, push things a little too far and see what happens. Stop flipping through magazines and see where your own artistry takes you. Stop listening to what people say/think for about a year and see what happens. Have some faith in yourself. A little courage. Be your own champion. You'll then realize that the "Is less, more? Or is more, more?" question is rhetorical. Rhetorical because it was meant to generate this conversation. But beyond rhetorical, the question is actually irrelevant. Because it is whatever you want it to be. You can be as "more" as Joel Grimes. Or as "less" as Richard Avedon. Those guys don't ask themselves, "Have I gone too far?" or "Have I gone far enough?"
They just go.
And we love them for it.