In China they have been used for years as a tonic for male infertility. Mainly in part due to its ability to modulate testosterone production.  In boutique Chinese supplement stores, you'll often find ornate jars of Cordyceps locked behind a secure display case - one normally reserved for items like diamonds and firearms.
For the wild (most potent) strain of cordyceps, they cost more per gram than gold or even cocaine to be put into perceptive.
Stress has little or no benefit in modern society and any stress that can be removed from day to day life is a good thing.
Taking adaptogens on a daily basis will increase your quality of life and productivity. Here's why
One of many great talks by the author:
I can't remember how Polanski said the cortisol response changes in response to chronic stress and burnout. In a quick search I turned up some papers saying that burnout involves higher waking cortisol, but then there were others like this indicating that a blunted response can also be a dysfunctional state associated with various problems getting through life in general in a productive way.
So one question might be: is it elevated or depressed cortisol that we're trying to deal with? Or some other part of HPA function, since that system seems to be pretty well established as a central one in chronic stress? It's possible there's a well-researched answer already out there and I just didn't turn it up in a quick search. The answer lies in the stimulatory effects of cordycepin, which is analagous (structurally similar) to the human nucleotide Adenosine. 
Another question that I think is at the root of what you're asking is whether most of us are chronically stressed enough to benefit from adaptogen use. I think the answer to that is most likely yes. One piece of evidence for that is how many people see huge benefits from stress relief through massage, yoga, meditation, and how many people self-medicate with alcohol, marijuana, opiates, etc. You could also think about how many people you know that really satisfy the criteria for a low-stress life: do they get enough sleep, have a supportive social network, a sense of control over their lives, respect, a sense of purpose, the chance to have worked through any trauma from earlier in life, etc.? Some people have some of those but I would bet it's not a big group in the intersection of all of them. The question then would be whether adaptogen use could be sustained over a long enough time that we could sort out some more macro-level factors in our lives so that we can reduce the baseline level of stress and with it the need for long term adaptogen use past the point where tolerance might lead to diminishing returns.
 Chang Y, et al Effect of Cordyceps militaris supplementation on sperm production, sperm motility and hormones in Sprague-Dawley rats . Am J Chin Med. (2008) (http://www.ncbi.nlm.nih.gov/pubmed/19051352)
 Leu SF, et al The in vivo and in vitro stimulatory effects of cordycepin on mouse leydig cell steroidogenesis . Biosci Biotechnol Biochem. (2011) (http://www.ncbi.nlm.nih.gov/pubmed/21512251)