Man if you find some good data, please post it here. There's a real shortage of study on the effects of short-term (week or less) exposure to high altitude, and the anecdotal evidence seems to vary greatly by individual.
While researching Leadville 100 strategies I did see a paper with a sample of 5 referenced that did show a positive result from about 3 days of acclimation. As a result of that paper I then read of several 'experiments-of-one' reported by folks who thought the type of trip you're taking did help. One thought it was "jump-starting" their acclimation, another felt it increased their acclimation, and based that on Heart Rate.
Not too specific, I'm sorry, but like you I haven't found much specifics. I'd say try it, and personally I'd caution against going too hard in those days leading up.
Lastly, here's a link to the recommendations from a residential high altitude training facility about preparing to come to altitude.
Best of Luck!
In response to:
So… I’m considering a short backpacking trip before the PPM, with the idea of sleeping at 13,000 feet on August 14, 15, and 16. (And then sleeping in Manitou Springs on 17 and 18.)
The questions is, will these nights at high altitude just a few days before the race help or hinder race day performance? Is this too close to the race that my body won't have any time to adjust in any beneficial way? Will it actually have a negative effect?
Ordinarily, I live at 6,000 feet, and aim to run and backpack in the high country a fair amount over the next 6 weeks anyway…
Any advice on the wisdom of those 13,000-foot nights greatly appreciated!