Looking at 1968 as a continuation of 1964, is really inaccurate. To best understand Nixon's strategy you have to read Kevin Phillip's "Emerging Republican Majority".
1968 was a continuation of the process that started in 1948, and that was to absorb the Thurmond "Conservative" wing of the Democratic Party in the South as this shared most everything in common with the Republicans (FP, hostility to the New Deal and so forth), and the only reason they had remained Democrats was race as they saw Democrats as they only means by which to assert themselves and maintain control. The problem is that you have to win them without appearing to be crossing the lines. This is my analogy not Phillips, of Goldwater's strategy amount to crossing the lines, putting on a grey uniform and waving the Confederate flag. This was not going to fly in the border states where the GOP depended on unionist mountain support, much less in the rest of the country.
That is where tough on crime comes in as the perfect message to unify the Republican base in the suburbs of the Midwest and West with the "emerging ones" in the suburbs of the South. This way they could still come off as the party of Lincoln to those for whom such made themselves feel better about it while at the same time throwing enough of a bone to the Thurmond vote to make them vote Republican (this is where the 30% comes from naturally as well as the narrow SC win) based off the rest of the issue pie.
To the less conservative, more populist rural areas though, this was not enough and that is why Nixon lost this vote to Wallace. Remember Wallace himself had been "out-segged" in the 1950's and was determined to not let that happen again. Furthermore, going all out on race and segregation was the standard tool for the "business/conservative" wing to survive in primaries dominated by poor farmers on the state level (though obviously low turnout and jim crow voting restrictions skewed these elections to the wealthy it didn't lead to complete domination outside of the black belt and urban areas where most all of the poor were blacks thus creating the most extreme wealth skew in such places). However, Nixon couldn't go as far as Goldwater much less as far as Wallace so they were kind of screwed in the rural areas, though Nixon did win the Southern suburbs according to the exit polls if memory serves me and those places along with low country would become the GOP base over the coming decades, and be the first areas to flip down ballot.
However, Wallace won almost all counties in the states he won. Nixon didn’t win a single county in Alabama, Mississipi, or Louisiana and only one a few northern counties in Georgia.
