His endgame was self-aggrandizement. He's a rather slippery figure and it's difficult to get a handle on his intentions, but political ideology was never a big concern for him. The governor of Louisiana, Miro, wanted him to go back to Kentucky and play up the idea of a break from the US and merger with Spain. By making this deal he opened the Mississippi to American commerce, which made him a big hero in Kentucky. Miro had granted him a shipping monopoly, which meant he would be able to transport others' produce. I think it was this local standing that he was looking for. He knew very well that no one in Kentucky wanted to live under the Spanish crown.

He told different stories to different people. I don't even think his "conspirators" knew exactly what was up. The high point of his influence was the statehood convention of November 1788, of which he was the chairman, where he proposed that Kentucky unilaterally declare independence from Virginia and work out a separate deal with Spain regarding the Mississippi (which was by far the biggest hot-button topic in the region). His ideas were entirely rejected and never revisited. I think he strung the Spanish along so that they would continue to pay him.