From what I can gather, many people who like the Blu-ray admit that there is a push towards blue, cool tones compared to previous releases, but that it's accurate. Screen caps notwithstanding. They know this due to living memory and Disney's own account of how they graded the image.
Many feel that the image is brighter, but that it's accurate (i.e. less 'muddy'), for the same reasons.
Others, like myself, don't know, but have doubts based on experience viewing Technicolor images. I must be among the 'colour blind' ones.
To me,Technicolor creates vivid primary colors, red, green, blue, etc. I see this from numerous other releases from the same or similar periods, including yes, The Ten Commandments, which looks fine to me BTW, and which also has a very strong blue palette during long portions. I don't see that in Mary Poppins. I see primary colors bled from an image that favors blue.
The screen caps posted here probably represent exaggerations in one form or another on each end of the spectrum, but I believe the basic changes to the image in 2013, whether right or wrong, are fairly well represented.
I also wish I could live the life of the content with the knowledge that everything is right with the Blu-ray based on 50 (or 40) year old memories and the statements from a press release. Life experience has taught me to be a bit more skeptical and think for myself.
I feel pleased for those who feel that 'this is it' regarding the accuracy of this particular title. I wish I could share your enthusiasm.