I didn't have a Blu-Ray player when these first came out, so I didn't bother buying them back then. Now I have one, though, and the other day I found these in a bin at Wal-Mart for about $8 each. Watched them both, one last night and one today, and enjoyed the new features, but mainly savored the excellent picture quality.
On the Labyrinth Picture-in-Picture commentaries, it seemed like they chose two people specifically because they appear in lots of Harry Potter documentaries: Warwick Davis and Nick Dudman.
I still only have these on DVD, but based on some of your comments, it seems like they are worth picking up on BR as well. Aren't there a few different versions floating around now, years later? I noticed a Froud art edition with both movies packed together as well as a DC Steelbook from Germany. Is one version better when it comes to BR? I'd personally like the option with the most deleted scenes, etc.
I finally got around to picking up Dark Crystal on BR and its gorgeous. I noticed so much more detail in HD, they certainly cleaned up a number of scenes. I also enjoyed the Brian Froud commentary. Even simple things like the menu are so much better compared to the DVD - great purchase.