Reagan's justification for invading Grenada was that he was protecting the hundreds of American medical students studying in Grenada.
The Crimea was part of Russia until 1954. It had, and still has, a massive Russian military base there. In 1992 Ukraine officially recognized the Crimea as largely autonomous. So in that light, Russia has much more standing to go into the Crimea then Reagan had to go into Grenada.
I did not want to imply that the comment is irrelevant, it shows, as you say, an interesting parallel in the way of thinking. I wanted to say that it is completely irrelevant as a justification for the current actions of Russia.
The Crimea was part of Russia until 1954. It had, and still has, a massive Russian military base there. In 1992 Ukraine officially recognized the Crimea as largely autonomous. So in that light, Russia has much more standing to go into the Crimea then Reagan had to go into Grenada.