You’re right about pretty much everything except one thing. Many are speculating with their savings, not on margin.
I expect that professional investors who specialise in Spanish property, understand the market and know what they are doing can still make a living out of it, though nothing like what they made in the past. But amateur overseas speculators buying off-plan in Spain are just desirous of loosing money. Amateurs seem to specialise in buying the wrong kind of property in all the wrong places.
If you are considering speculating off-plan, and someone tells you that failure to sell on “just doesn’t happen” then you know it’s time to walk away. For a start you can be fairly confident that they won’t be there to help you sell on. Sound familiar?