Take note, Mark.
My weather site has grown slowly over the years (since 1999) and really was a mishmash of orginal hand crafted code, code from an OS/2 WYSIWYG HTML editor and laterly Mozilla Composer. It did gain a style sheet a couple of years ago that helped a bit but any other changes of a vaugely site wise nature where just a PITA.
I've nearly finished moving over to a PHP based system and co-ordinating the stylesheet better. Site wide changes are now nearly all down to editing just the relevant file, not each individual page. I get the feeling stuff loads faster as well but I can't think why the server has much more work to do...