[pmoriarty]

> Note he doesn't state whether the difference was positive or negative.

But if taken (as it usually is) as a metaphor of life's choices, in this case his life choices made him Robert Frost, the famous, incredibly successful poet -- so it's implied that in his case taking road less traveled by was positive.

Now, if the subject of the poem was some anonymous nobody, then maybe the poem would be more ambiguous.