I upgraded the site to Movable Type 3.34 today and installed mod_fcgid, a FastCGI implementation, which should hopefully provide a few performance improvements.
I wish it was easier to merge the latest versions of the default templates with my older versions, which I've customised quite a lot. Unfortunately, the new templates make use of a radically revised set of stylesheet classes, so it's not possible to cut and paste my customisations into to the new templates. A lot of work would be required to figure out how the new ones work and it's just not worth it for a site like this.