Why do you think people are hoarding land today that could be used for housing developments and leaving it empty?
What is "too much" land that would subject it to your exponential taxation?
In short, you're just making things up. I'm glad you aren't in charge, though there are a concerning number of people with your mindset.
Spain is one of the last places on Earth I'd look to for economic policies. Enjoy your even higher unemployment and additional dying towns after attacking your only notable industry (tourism) I suppose.
There's plenty of housing available in places with no jobs, so mission accomplished in one sense!
Enjoy all the housing you could ever want when your town has even less economic activity than it did before!