I haven't tried tearing down the database between scripts. I use the method you described. However, I think the only fixture data you would need is whatever you already have to create a new database (in my case, a script that drops and recreates the tables, and fills in lookup values). The test-specific data is added by the test in either approach.
Even with an END block, it's possible for your test to die in a way where it won't be able to effectively remove the data you added. That's what makes this approach unsafe for use on a production database.
It's still faster than dropping the database and recreating it, but as things got more complex, I spent a lot of time troubleshooting problems with deleting the test data, and I think it would have been wiser ultimately to trade a little test speed for the saved debugging time.
Another wrinkle is web testing with Mechanize on code that creates data. If your web tests cause data to be added to the database, it won't be in your stack to delete, so you end up with manual deletes, and END blocks that complain and crash if the script dies before the data was added. It gets messy.