(2) Yes, FP2003 is well worth the upgrade.
(1) For anticipated global changes, FP2003 uses the model of "including one page in another", which actually includes parts of pages from independent files.
So, for example, you can make a footer file which is maintained in one place and inserted in all the pages of a site, with relative references automatically fixed up at insertion. You write it as a webpage in html and give the page fragment a filename (such as "footer.htm"), even if you never use the page independently and only use it as a fragment to be included.
Then in each page where you want that code included you just write its name in a special comment, like
<!--webbot bot="Include" U-Include="includes/footer.htm"
which means to copy and "relocate" all the code within the <BODY> tag of the page "footer.htm" in directory "includes".
A single page can be assembled from over a hundred fragments in separate files, and a fragment can be used in hundreds of pages (in my personal experience) with very good performance. All of the includes are checked after insertion, so errors such as broken links are detected and reported (in the FP2003 site reports) before the site is uploaded to the server.
Unlike "server-side includes" which are done when a page is requested, "FrontPage2003 includes" assemble the parts of pages into the files once, before FTP'ing to the server. The server can be a Unix/Linux server or a Windows server, and does NOT need to have any FrontPage Extensions installed; the server doesn't even know that its static pages were assembled by FrontPage2003.
Microsoft has free online training which includes both of the above techniques: