>> I can't imagine using a boot this heavy any more for loads of under 50 pounds (such as on a NOLS course).
Actually, I've found that the best type of footwear for me depends much more on the terrain than the weight being carried. On the terrain I usually hike, LaSportiva Makalus are much more comfortable (for me) than a lighter pair of trail runners or boots, even when carrying very little to no load. If it happens to be winter, than the advantages are even more distinct. Of course, YMMV.
>> The fact that the Sundowner Summit DO offer a vibram sole and still eroded this quickly points to a quality control issue from Vibram, not Vasque, who contracts our with Vibram to make their soles.
Actually, as detailed in my post above, the sole of the Sundowner is the one part I haven't really had any trouble with (other than lack of grip on smooth rock). It's everything attached to the sole that has utterly failed. Also as I mentioned, the boots didn't totally fall apart after 125 miles (I still wear them daily, in fact), but they are useless as serious hiking boots, due to the abrasion holes and cracks in the last.
>> Still, a pair of boots in the style of the sundowner should be good for typically 1200-1500 miles (based on informal surveys of boots and shoes from my own AT through-hike).
They certainly should. Given how much knowledge you have in this area, your statement should be a stern warning to anyone who is interested in buying Vasque boots and is reading my experience with them. Of course, this is just my two Lincolns.