<p>You can upgrade the demo version into the retail version and continue your savegame without issues. <img alt="" data-src="//content.invisioncic.com/g322608/emoticons/smile.png.142cfa0a1cd2925c0463c1d00f499df2.png" src="<___base_url___>/applications/core/interface/js/spacer.png" /></p><p>
What you want is the trial to retail patch.</p>
Yeah, harder base game with a powerful editor as a tool for sandboxers, as well as powerful User Preferences, I think, is a good middleground way to go.