I'll give you my responses, Bronco. I've researched this quite a bit myself over the years, so I think my comments are pretty accurate. Hopefully you'll find them helpful.
1. "Is the WoW a commandment?" -- In the beginning, no. But now yes. Although an argument could be made that it was the will of God that the Saints follow it even in the beginning, else why would it have been given? And what is a commandment other than an expression of the will of God for us to follow? Anyway, as you know it wasn't a requirement for church members to follow the WoW at first. Brigham Young in 1851 went a long ways towards changing that, (if I recall correctly) telling the Saints that it was now the will of God for it to be a full-fledged commandment rather than just a suggestion. The implementation of the commandment was still not complete for another 50-60 years after that, when eventually Pres. Grant made adherence to the prohibitions a standard for temple recommends. The Wikipedia article has some good info on the history of the WoW, see http://en.wikipedia.org/wiki/Word_of_Wisdom if you haven't read it yet. I've got another, more complete source I can email you (a master's thesis on the topic)--if you're interested, send me a PM.
My take is basically, if you support Brigham Young as prophet and president of the church, and subsequent church presidents, then you support their ability to clarify existing revelation, and/or to modify them as times & circumstances warrant--including in this case to change the WoW into a commandment.
2. "The membership seems to practice (and the authorities allow) selective obedience" -- Absolutely. But I disagree with your "So, essentially, if you cannot "run and not be weary", you aren't living the WoW correctly" sentence. What about paraplegics, for example? Are you going to say they don't live the WoW correctly? Other counter examples are easy to find. So the "run and not be weary" line doesn't mean that in a literal, absolute sense. I agree that we should be very nonjudgmental towards others--and in fact when my high priest's group was discussing this a couple of months ago, several of the members expressed similar sentiments. I think one of them said something along the lines that "tobacco is one of my very favorite smells at church, because that generally means someone is trying to return to the fold."
3. "Interpretation of the relative importance of the WoW has changed over the course of the history of the church." -- Sure, see my comments for item 1 above. In addition to the "make a profit from tobacco" stuff at the UTLM link, I also have a relative who worked for a while as a trucker for a beer company. I also knew a man in Wisconsin who worked for years at the local brewery after he joined the church. Heck, I even had a missionary companion who worked as a bartender to save money for his mission! :-) As near as I can tell, it's the church's policy that it's sinful for *church members* to partake of the prohibited substances, because we've made covenants not to, but not necessarily sinful for others to do so. I personally do not judge nonmembers at all for, for example, drinking beer*--but I'm grateful for the teachings of the church that have led me myself to never try it. My grandfather was an alcoholic, fortunately sober when I knew him, and who knows? I could easily have ended up one myself.
By the way, I've browsed the UTLM website a lot, and have looked up many of their references. Unfortunately I've discovered they *frequently* take quotes out of context, and so I've stopped trusting anything from there. At most I'll google a quote from their website to see if I can find it anywhere else with more context. I'm not saying that the quotes are wrong in this case, just that I've stopped trusting them in general.
4. "Beer." -- I've had non-alcoholic drinks from barley before. I had a member in Germany give me a nonalcoholic beer, for example. And it seems like when I was growing up, my mom stocked Postum in our cupboard, which if I recall correctly is a barley-containing drink as well. http://en.wikipedia.org/wiki/Postum. So "mild drinks from barley" makes perfect sense to me.
Final remarks: Something that I think goes largely unnoticed, is that the period of time when the WoW went from being a suggestion in the church to an enforced commandment, ~1860-1920, is exactly the time period when refrigeration became available, first on the commercial scale and then for individual households. See http://en.wikipedia.org/wiki/Refrigeration and http://en.wikipedia.org/wiki/Refrigerator. Alcohol had substantial importance as a preservative in the time period when the WoW was given, but as electric refrigerators became more common, the need to rely on alcohol to preserve things was greatly reduced. I personally feel that's a large reason why the Lord saw fit to change the WoW into a more enforced commandment for the church during those years.
* but not to the extent of getting drunk