Here's my impressions regarding the Decca sides: there are imo some improvements to the sound from the source cds, but if you are buying the set for improvements of the Decca sides alone I think you'll be a bit disappointed. The Decca tracks that are sourced from non-CD sources do have a certain vividness to them that put them a bit over the others, but the homogeneity of the mastering is quite good from track to track and disc to disc.
The Una Mae Carlisle and the Sammy Price and the Commodore sides have never sounded better to me on CD. Also Clef, Mercury, Alladin and Philo sides etc. transferred from disc sound excellent.