They were done as straightforward 2K (1080p) remasters of the original master prints except for Wrath of Khan, whose master print had deteriorated and required restoration. The 2009 TWOK HD restoration took on an inexplicably blue tint, but that was corrected when they remastered the TWOK director's cut in 4K back in 2016 (a stand-alone release; the version included with all currently available with all boxed sets is the 2009 restoration of the theatrical version). So they're not upscales, but neither did Paramount do anything special to prepare those remasters.
I'm in a Facebook group devoted to TMP, and the folks there are really excited about the new 4K remaster, even for just the theatrical version due out next month, and general consensus seems to be that the 2009 remaster of that film sucked out loud. But if you're fine with "good enough," knock yourself out.
I wouldn't be against buying them a third time, in however many years, if they complete all 10 films in 4K. I might even be upgraded myself by then. But an improvement over the DVD's would be "good enough" for now.
Yeah, no way that set is legit. First off, Disney hasn't released any sort of big MCU boxed set for Region A, and the Region B boxed sets they've released have each film on its own disc.
There was The Infinity Saga box set, but I believe it was fairly limited and sold out in a short time and is listed for $1000+ on amazon and ebay.
See my answer above; I believe that was only TWOK that ended up with a blue tint. I haven't heard that complaint about the other nine.
That was probably what I remember. It's been a while and I know TWOK was discussed re: the blue tint.