In my experience, total solar eclipses generate an extraordinary amount of interest, and since only a very small part of Spain will have totality, expect it to be very, very busy. I would advise against relying on public parking spaces, as the authorities will implement very different rules on over-nighting, compared to the normal situation. I had the pleasure of observing the 1999 total eclipse - we chose a remote spot just over the border from us in France, expecting it to be a quiet, surreal experience. In the event there were probably approaching a thousand people there, with a fantastic atmosphere - it was one of the most memorable experiences of my life. Do go - you will not regret it.
But make it easy on yourself - book into a campsite, even if it is not really close to where you want to view the eclipse from. And book as soon as possible - they will be full. Don't worry about the cost - the memories will outlast the hole in your wallet!
