"The problem is that "strengthen the immune system" isn't just vague, it's virtually meaningless."
Vague and not well-defined terms and concepts are effectively non-existent and therefore automatically "virtually meaningless". This follows clearly from the logic of language and meaning. Your problem (and the vast majority of other people also seem to have it) is that you are not fully differentiating between the "technical terms" of a particular branch of science (or any other academic pursuit for that matter) and these same words commonly used in the vernacular language of everyday discourse.
Although relative to the science of immunology "strengthen the immune system" is definitely vague and therefore meaningless, I do not see anything wrong with that expression as a reasonable description in the vernacular language. To me it would simply mean that these ingredients decrease your likehood of infection or decrease the severity of an infection or both, and as I recall, there is some reasonable evidence that they do. The details of exactly how that is done are probably not fully known (as with so many things in immunology - just because it is so complex) and in any case are beyond the understanding of the WF customer (and likely anyone who is not an immunology expert). What do you want WF to do? - Baffle them with bullshit (technical jargon)!
"While there are PubMed studies, the current MedlinePlus (also an NIH branch) consensus is that there is insufficient information to draw a conclusion about the efficacy of goji berries."
By who's consensus? Are you a medical establishment shill?
"I'd need to see much more long-term clinical studies to be convinced. Right now, I see a handful of animal studies with varying claims."
Aw com'on now! And who is going to pay for these clinical studies? Are you looking for a grant for yourself or some other government worker? Look I will put up $300 of my meager funds , $100 for a clinical study of each one of those ingredients. Are you willing to do the same and how many others do you expect we can get with the tax burden already imposed on so many - some of which is going into your pocket as a government employee!