So long story short, yesterday I ended up with a copy of Mono Masters thanks to a broken street date and a stroke of luck. [Though apparently there were some to be had in stores this morning for a bit cheaper than I ended up paying, but with that being unknown until doors opened this morning I basically paid for insurance.]
They are definitely not numbered. Boo! They are, however, gorgeous. Are they worth it? Absolutely - the packaging alone is beautiful and you really feel like you're holding something special in your hands rather than just something that was thrown together. [That said, they really could have numbered the sleeve of the White Album like the original run, but that's a minor, minor complaint.]
Comparison shopping - do you need both mono and stereo versions? Let's deep dive into 'Magical Mystery Tour', shall we? [I should note that I'm on my 7th listen to the album in 48 hours as I type and it's still exciting. Make of that what you will - perhaps I'm just easily amused.]
Song by song breakdown:
 Magical Mystery Tour - Honestly, I don't notice much difference between the mono and stereo mixes. Maybe this isn't necessary...
 The Fool On The Hill - I described before how bright and full this one is on the new stereo master. It still sound better than ever in mono however it doesn't "pop" as much, track cluttering and all that. Score one for stereo.
 Flying - To my ears the instrumentation is slightly different in mono, particularly the ending loops, but neither stereo or mono has the edge.
 Blue Jay Way - In terms of clarity stereo is the clear winner here. [See what I did there?] However, that's not really the point of "Blue Jay Way". In mono it still sounds nice and spruced up thanks to the remaster but retains more of its haze and mystery. It's all tied up now.
 Your Mother Should Know - This is a toughie. Even more than "The Fool On The Hill", "Your Mother Should Know" positively shines in the new stereo master and if you were judging each song individually, this would win hands down. However, in mono there are lots of neat little effects and piles of reverb near the end that aren't present in the stereo mix. While it might not fit the song as well, it ties it in nicely with the rest of the album and is very appropriate for it as a whole. I kind of doubt you're ever going to say to yourself: "You know what song I really want to listen to right now? "Your Mother Should Know". If you were, the stereo mix would be the one to go to as its pretty much perfection. In the grand scheme of 'Magical Mystery Tour', however, mono wins.
 I Am The Walrus - Another six-of-one-half-dozen-of-the-other instance. I voiced my complaints about the stereo mix yesterday and those issues are not present here. No sudden aural snaps, no obnoxious constant left/right panning in the fade out, no terrible stereo separation distracting from the song. That said, the mono mix is very clearly derived from a different take than the stereo mix. There are two very, very obvious differences: Ringo's drum fill before the second half of the first verse is totally gone and the backing track all but drops out about 1:20 into the song before John's first extended "I'm cryyyyyyying" leaving only vocal and strings. Not really huge differences, but if you grew up on the stereo mix you're going to notice it and it might be distracting. Neither mix is perfect - unless, of course, you're used to the mono mix - so you kind of need both here.
 Hello Goodbye - I didn't notice any big differences.
 Strawberry Fields Forever - HUGE improvement in mono. Every part plays nicely together and the genius of the song is back on display here. Not even a contest, mono wins. That said, the first fade out/in is much quicker in mono and the second fade out starts much earlier though the song lasts the same amount of time. Not as dramatic as the "Walrus" changes, but noticeable.
 Penny Lane - Not as definitive a victory for stereo as mono's win on "Strawberry Fields Forever" but it is still the hands down winner. The mono mix just sounds flat. If you hadn't listened to the stereo remaster yet you probably wouldn't know what you were missing. However, this track is one of the shining examples of what a good remastering job can do on the stereo disc.
 Baby You're A Rich Man - Mono wins again for the same reasons it won on "Strawberry Fields Forever".
 All You Need Is Love - Slight fidelity differences and different instruments higher in the mix between the two versions and an earlier fade, but nothing major. [No "She Loves You" at the end though? Or did I just miss it?] Not one of my favorites to begin with so I'm not particularly bothered either way.
So make of that what you will. In a few month's time when the shine of the new has worn off I honestly don't know what version of this album I'll reach for. On headphones it will be the mono mix no question - the stereo separation is way too distracting that close up. On a good set of speakers, though, the slight differences in the mono mix would probably be enough to draw me back to the comfort of the stereo mix.
On a similar note, the mono mix of 'Sgt. Pepper's Lonely Hearts Club Band' is also considerably different from the stereo mix and, in my opinion, stronger for it. I haven't listened to the new stereo master yet but I almost don't want to - my appreciation for the album grew immensely after listening to the mono and I will certainly use that as my go-to 'Pepper' in the future.
For the record, the first five albums are just fine in mono - 'Help!' being the only one that was in stereo on the original CD issue anyways if I'm remembering correctly - so these will work for me. [I can't tell you the last time I listened to, say, 'Please Please Me' prior to the box yesterday and I can tell you I'm not in any hurry to put it on again.] 'Rubber Soul' and 'Revolver' have me torn - they both sound great in mono, however I just know that they're going to be bigger and better in stereo. However I don't believe there are any major mix differences between the two - please correct me if I'm wrong. I'm also undecided on the Past Masters set - everything bar three tracks is on Mono Masters so dropping another $17 seems silly. However, two of those missing tracks are the a- and b-sides of one of my favorite Beatles singles, "The Ballad of John and Yoko" and "Old Brown Shoe". Since I've already spent well over $300 on this project I think I'll be holding off for now. Christmas is coming, after all...