I have to say that language in this space evolves rapidly - a “demo” is not just a “demonstration”. It’s a usuable thing that allows you to get the feel of a game. I’m not sure people would like to pay money for an indie game when they can’t even try out the controls. And I’m pretty sure you’ll get a lot of people miffed at downloading an 11MB “demo” and finding they can’t actually play it. Noone calls things “playable demos” any more, as noone produces unplayable ones.
If you want to stop the freeloaders, have you thought about generating free reg keys that function for a limited time? Provide a form people can fill in to get a key emailed to them, and don’t let people apply if you’ve already sent one to that address. Or allow a maximum of three keys or something.
Don’t worry about people with multiple email addresses - they’ll run out eventually, and they’re obviously very keen on playing so leave them to it. You need to take care of people who own domains though. Maybe you need a summary of all domains who’ve had ten key requests in the last week, which you can then visually scan for any abuse every week or so.
Just a few thoughts.