Why Spanish entry into the Axis would add wrecks, not sea power

What could Spain have contributed at sea if it had joined the Axis?

Very little: the Canarias-class cruisers were the best option but were unlikely to survive, while war with Portugal could become an additional Axis burden.

In this counterfactual, Spain would contribute more shipwrecks than durable naval strength. The Canarias-class cruisers were its best available major units, but they were unlikely to last long against Allied opposition. Spanish entry could also imply an invasion of Portugal. Rather than strengthening the Axis, that campaign might create another front demanding German troops after Spain failed to win quickly.