Importing old data/validating existing/repairing

Is there a way I can import data from an old installation? I do know I can export data to an SQL file and import that one - BUT if I do that, my Piwik turns over on its back and dies on me. Can I validate the data in any way and perhaps repair them?

This happened after an upgrade from 1.2.1 to 1.3 and didn’t improve after upgrading the 1.3 to 1.4.