This link will take you to a site which lists around 175 public facing websites all hosted on MOSS 2007.
These will demonstrate the art of the possible with regard to the look and feel of a MOSS site.
My employer developed a combined Web Site and Extranet for Virgin Vie at Home (http://www.virginvieathome.com). When you view the site you will notice two login options on the menu at the bottom of the page, these provide secure access for two separate groups of users; customers and sales consultants.
In your post you do not specify whether you are considering Windows SharePoint Services or Office SharePoint Server. Both can be used to create publicly accessible web sites, or secure Extranet sites but there is a huge difference in functionality and cost. Typically one would be using MOSS for the public facing web sites. The intranet based team sites and the Extranet could be either.
WSS is free in terms of licensing, but you will be limited with regard to the functionality and look and feel.
MOSS will provide richer functionality for web content management which could address your problems with maintaining two sets of content. But has a license cost in the region of £20k per server for public web sites.
If you are providing sites for the public sector then you may also face issues with Accessibility. Out of the box SharePoint does not deliver accessible sites. AA compliance can be achieved but with additional expense and effort.
MOSS is designed to address exactly the types of scenario that you describe and once set up it would provide a powerful and user friendly environment. I would strongly advise that you seek experienced support in making your technology selection. If you decide to go the SharePoint route then you will almost certainly require the support of a professional services organisation such as a Microsoft partner to get set up. The Partner Directory on the Microsoft web site could be a useful starting point.
I would also recomend that you consider breaking the project into distinct phases. You could begin with the Intranet and workout through the Extranet then the Web site, or begin with the Web site and work inwards. Doing all three together would be a huge challenge.
Hope these quick comments are of use.