Reagan was as good an extemporaneous speaker as you could find. And the ideas he put forward were as much his own as of his speechwriters, aides, etal.
This was NOT true during his presidency. His ability as an extemporaneous or impromptu speaker took a serious turn before he became president. During his presidency, Reagan
usually worked from a script and did not depart from it. When Reagan DID depart from his script, the result was often clarifications or retractions from the White House, if not outright shameful gaffes.
There are quite a few books about Reagan that discuss these incidents:
- Reagan read part of his stage directions as part of his speech and never noticed it.
- Reagan read a speech in which the word "paradigm" was used, and it was a word he'd never heard before. He pronounced it "para-dijum."
- Reagan, when speaking unscripted, repeated false stories, including stories about welfare abuse and capital punishment in England.
- Reagan used the same off-the-cuff remarks, almost word-for-word, in different interviews.
- In remarks he composed himself, Reagan addressed a gathering of Medal of Honor recipients and recounted the tale of another recipient, but the tale was false (it may have been based upon an amalgam of a movie plot and a WWII scuttlebutt, but it was not a legitimate Medal of Honor story).
- Reagan got thrown a question he could not answer and stood there doddering until Nancy prompted him on how to answer it.
- Reagan could not ask intelligent questions and asked people to give him written copies of their presentations so that he could go over them at his leisure. (He did this when outgoing President Carter tired to brief him on the important issues he would be facing.)
- During the debates, and especially during the debate with Walter Mondale, Reagan showed he could not answer extemporaneously. (Before his debate with Carter, Reagan's folks obtained a copy of Carter's playbook so that their guy would have scripted responses to what Carter was expected to say.)
And there are many more. In the latter days of his presidency, Reagan gave up giving news conferences because he couldn't improvise at all. In the scripted speeches he gave, he often seemed lost and confused.
Now, his official biographer noticed these trends as well, and attributed them in part to the shock to Reagan's system that came from the assassination attempt early in his first term. But Reagan was slipping even before that. On his first day as President, Speaker of the House Tip O'Neill mentioned Grover Cleveland's desk, and Reagan responded that he (Reagan) had played Grover Cleveland in a movie. Stunned, the Speaker corrected Reagan, saying he had portrayed Grover Cleveland Alexander, a baseball player, not Grover Cleveland, the US president. The Speaker would later say publicly that he could not discuss anything with Reagan off the cuff, and that Reagan was the least informed on every subject of any president he'd ever met.
Would Reagan have read the wrong speech? Hell yes. Even his own people thought he would have, if he'd been in the position that Clinton was in.