Embargoes have never work. This is to pacify the U.S. hyphenated Cuban-Americans (voters) who themselves will try and make a beeline to Cuba to take over once again when Castro is no more.
You are correct. We are the only country not trading with Cuba. But, and here is the interesting part, Castro still gets a lot of good from the U.S. Some business people in the Free Zone in the Republic of Panama order all kinds of goods from the U.S., bring it to the Fee Zone, and reship it to Cuba. In the eyes of the U.S., it is not illegal to ship U.S. goods from a third country. In the end, the goods appear to go to the "in" crowd as apposed to the Cuban on the street. But the point is, U.S. goodies are shipped to Cuba. And yes, we should do what W. Germany did to E. Germany. Do it directly rather than through a third country.
The communist regime fell not because we sent Coca Cola to them, but because of the extraordinary human cost and economic disaster that formed the core of the system. The dismembering of the Soviet block was precipitated by the strong policies of Ronald Reagan. If the policies of appeasement that you propose for Cuba were followed, the Soviet Union would have been still in power sustained with our taxpayers’ dollars.
Your proposition is naïve, Castro only buys on credit, if he had money or credit to buy elsewhere, and he would never buy anything from us. The problem is that Castro has defaulted on his debts and the smart entrepreneurs who thought they were going to do a quick and easy profit exploiting Cuban cheap slave labor were cheated. If he is now offering to pay cash in advance is just in order to erode the embargo. Once he pays a few small purchases in cash, he will demand the opening of credits. The same tactics used by conmen all around the world.