Celia, it is a great idea! And apparently you are not alone - it sounded familiar, and I did a search, and discovered an article MM found and posted about the same idea. You can read it here:
http://www.madridman.com/ubb/Forum16/HTML/000008.html It sounds like it was happening in Barcelona. But what about Madrid? You're so right about people working in Madrid and living far away. Turn around, and another ciudad dormitorio has appeared, along with the added traffic jams.
I think it's a wonderful idea! I wonder how business is going in Barcelona... It may be worth looking into...