I've used the API this time, and that allows me to map each tag to exactly the right target URL without upsetting the appearance of the tag cloud - I was also able to edit the list so that one composer (James Oswald) did not overpower all the others.
The XML is really simple - I generated it from a single SQL statement.
When I have time I will improve it so that composers I want to highlight (e.g. this year's anniversaries) come out in a different colour.
Then it will be time to decide whether this is actually any use to potential website customers or not! But I do really like this technology, it's so simple to use.