Very right in your post #61. The term came out of the black racial movement in the 1960s 70s, when the Dems realized that controlling an “ethnic” block was the way to power. Actually, they already knew that and had long been famous for practically being at the dock to meet incoming immigrants, managing to snag the Irish and the Italians as Dem blocs.
So “defining” and consolidating the various and very diverse people from Spanish speaking backgrounds into a Dem-controlled identity was very important. They couldn’t even figure out what to call this new group at first. Oh - another amusing thing - Spaniards were excluded from this identity.
SPOT ON and I know all of that, but others here may not, so thanks for posting what you did! :-)