Gionni Dorelli: can we upgrade from version 2?
Yes, you can even upgrade from version 1 for the same price as version 3.
Roman Korcek: Does anyone know what has changed between the beta and the final, please?
according to this link, there have been no additional features added to the beta this time. only computing performance enhancements. and the ability to upgrade your LR3 catalogs to LR4, but that was a given.