> I'd imagine placebos are getting more effective due to more people having purely headspace/mindset (or even imaginative) illnesses/causes due to stress factors

Here's a list of medical conditions studied by placebo treatements: http://en.wikipedia.org/wiki/Placebo#List_of_medical_conditi... Many of them had significant positive results for the placebo.

You could argue that many of those ailments could be due to mental/stress issues, and that it makes sense that calming the mind and believing in a treatment would work, but for some of them (Parkinson's, Herpes, food allergy), it's pretty amazing at how individuals are affected. Maybe we're under-crediting the brain's ability to control the body.