In spite of his crypt-keeper image, Goldwater was very charismatic and certainly a better orator than Johnson.
However, he was still Barry Goldwater- a conviction politician. He was who he was, nakedly and without pretension or condescension, and had to be accepted or rejected en bloc, more like Coolidge or Thatcher than any post-New Deal President. And who he was was somebody who was unpopular during the high-water mark of postwar liberalism. To make Barry Goldwater POTUS requires a POD early enough that a man like Barry Goldwater can get elected in the first place.
If Johnson agrees to debate Goldwater, Goldwater would do quite a bit better overall, probably have some pickups in the Mountain West, Great Plains, and Outer South, and '64 would not be remember as a major trouncing, though it wouldn't be close.
Interesting effect: The Deep South went for Goldwater as a protest vote, as he voted against the CRA. If he clarifies his position better in the debates(he was in favor of integration, he just wasn't in favor of the federal government doing it, especially not to private businesses) he'd probably do as badly as Johnson in the Deep South, which would go to a Southern protest candidate, most likely everyone's favorite piece of human garbage, George Wallace. Meanwhile, in relatively close VA+FL, Goldwater could pick them up in the 3-way race.