The BD copy has a pretty consistent 30Mb/s bitrate and DTS Master Audio in 6.1. I found it to be superior to the HD-DVD, which only has standard DTS-ES and a lower video bitrate. Both have Dolby TrueHD, but I think it is 16/48 vs the 24/48 for the DTS-HD-MA on the BD version.
So, yea, it's worth the upgrade. They did a new encode for the Blu-Ray rather than just use the same data...which would not warrant an upgrade.