Well it didn't quite take all night. But I'm happy to have changed the template over and managed to keep in all the essential things that were in the old version. The key to this is backing up the old template and then using bits of it in the new one. (Some non-essentials have been pruned.) I haven't yet worked out all the expressions in the new style template but have got my head round the idea of the variable definitions at the top of the template. Not sure I like them all that much - I am happier just putting in the CSS as and when - the variables seem to be used all over the place for non-obvious purposes - like when the date title gets put in the border colour. Anyway, I think that the look and feel is OK to start with.
When I get another chance to tinker, I might try some of the ideas on sites like the Blogger Hacks Wiki, the Hackosphere and Freshblog.
I'd like to sort out the blogroll a bit - put in some categories and headings - which can be done easily enough with Blogroll itself by sorting the entries into different blogrolls and then posting them with appropriate headings.