Nice to hear from you. There is, however, a point or two that I was evidently not clear enough on. I'll combine clarifying with a reply to your message.
For those who may be less used to the cold than you are, we should point out that there is "cold-wet" and "cold-dry". The difference is in whether you expect your boots to be able to get wet from the outside (e.g. temperatures in the 20's and wet snow vs sub-zero(F) and dry snow that will not be melting on your boots).
When you think of the boots you are going to wear in the cold, and how you are going to use them, you need to distinguish between those two kinds of cold. What is at issue is *how* you are going to have the dry insulation you need -- either way, you need to understand how you are going to keep the insulation for your feet dry for the trip you plan. If you cannot do that, then the boot is unsuitable -- you will risk freezing your feet.
There are three basic kinds of insulation: encased in something securely waterproof (e.g. Mickey Mouse boots), removable (e.g. felt liners) and none-of-the-above (i.e. non-removable insulation that is exposed to water either from the outside or from perspiration.
Mickey Mouse boots are an example of cold-wet footwear, and mukluks are an example of cold-dry footwear. Will reports that "The Tundra is a boot for serious cold" -- i.e. cold-dry.
MOISTURE ACCUMULATION: I agree with you that there is no such thing as a non-waterproof lining that will keep the insulation dry if you are out for an extended length of time. A WPB liner is false security -- all that will happen is that the vapor that gets through it will condense within the insulation when it gets to insulation that is at the dew point -- resulting in wet insulation.
The fact is that you must either (a) keep the moisture from the insulation or else (b) be able to dry the insulation (which probably means removing it if you are camped out).
Since the Salomon has non-removable insulation, you (probably) won't be able to dry it on on a multi-day trip, so you must keep it dry to begin with. The only way I know to do that is vapor barrier socks. As you have noted, no socks are needed for warmth inside the VB, but most people agree they are definitely needed for comfort. IMHO you should go with the thinnest ones you can that will still allow you to feel comfortable -- the reason is that thinner socks are easier to dry, and if you are out for an extended period you will probably want/have to dry them. Warmth is not an issue -- that is being provided by the boot's insulation.
VB SOCKS: I am not thinking of them as keeping you warm -- I am thinking of them as keeping the boot's insulation dry, so that the insulation will continue to keep you warm. They are good in any degree of cold that would result in condensing perspiration inside your insulation. For example, I would not consider upper 20's to be "really cold", but I sure do want to keep my insulation dry at that temperature.
As to changing inner socks, the main thing is foot health (it is not good for the feet to be permanently wet). Wet inner socks should not be making your feet cold, at least as long as the boot's insulation stays dry. If the wetness makes you uncomfortable, though, then change them.
My own experience (both personal, and those I traveled with) is that wet socks inside a VBL were not a problem all day long, so long as feet were dry and warm all night long. See my further comments below.
SLEEP WITH BOOTS ON: I never intended to suggest that! Sorry I was not clear enough. The only folks I know of who need to do that are soldiers in cold weather.
What I *did* mean to say is that in serious cold weather, your boots belong in your sleeping bag with you at night -- in a waterproof stuff sack if needed to keep the sleeping bag dry. The intent is to keep them from getting cold-soaked and (if they are at all damp) frozen stiff. I hear your objections to boots inside the sleeping bag -- all I can say is that I have spent a *lot* of nights with Mickey Mouse boots inside my sleeping bag (but not on my feet).
The only folks I knew who did not sleep with (not in) their boots just about froze their feet in the morning when they had to wear cold-soaked boots. It was also very hard to put such boots on -- you had a damp sock trying to slide along a cold-soaked surface -- the socks tended to freeze to the surface, and act very sticky as you put the boots on. I have seen people ram their toes through the toe of the sock trying to force it into a cold boot! People who did that once tended to sleep with their boots thereafter.
HOW THE ARMY DID IT: when I was in college, I knew a guy who had been an officer in the Korean conflict (which gave birth to Mickey Mouse boots as the solution to an unacceptable rate of frostbitten feet among the soldiers). They, of course, had to wear their boots 24x7. The problem with that is avoiding trench foot, since your feet are constantly wet.
What they did was to stop every so often (I think it was every 4-6 hours), take their boots off, wipe out the boots, dry their feet, use foot powder if so inclined, put on dry socks, and put their boots back on. They fastened the socks they had just removed inside their clothing, so the socks would have a chance to (pretty much) dry out.
My own (civilian) experience with Mickey Mouse boots is that my feet being dry overnight prevented any problems. I wore the boots continuously from getting up (at daylight or before) to going to bed (at dark or after). I did not find the need to change socks during the day. I did dry the socks overnight (but not on my feet).