The Spanish Empire, had won by some miracle the war, would be just Cuba, Puerto Rico, the Philipines and the African posessions, nothing compared wit hthe British or the French Empires. If by some chance it had not imploded between 1898 and 1914, there would still be little reasons for Spain to join. No one helped them IOTL 1989 war, so, why bother? What would be France or Germany ready to offer to gain their friendship?
Adn yes, the USA would still be going on. Their defeat in 1898 would be like the British defeat in the Sudan in 1885. They came back in 1898 and crushed the Mahdi.