Could it not also have been partly due to earlier scientists underestimating the degree to which qualitative phenomena derive from quantitative phenomena? Their error, then, was in tending to assume this quality was immune to study, rather than in assuming the quality itself. Since you can say "Why? Elan vital!" to any possible observation, it is equally good at explaining all outcomes, a disguised hypothesis of maximum entropy, etcetera. But you say earlier 'Elan vital' was greatly weakened by a piece of evidence. In that light, it's hypothesis could be stated "the mechanisms of living processes are of a different kind than the mechanisms of non-living processes, so you will not be able to study them with chemistry". This is false, but I don't think it's entirely worthless as a hypothesis, since biochemistry is noticeably different from non-living chemistry. I think 'elan vital' makes some sense, even in a modern light. Most of the reactions in our body would not occur without enzymes, and enzymes are a characteristic feature of life. So perhaps we can say that 'elan vital' is enzymes! There is at least one experiment I can think of that could have been interpreted to show this too: I believe it involved fermentation being carried out with yeast-water (no living yeast, but clearly having their enzymes).

I'm reminded of Emotivism. "Belief in belief" sounds perfectly plausible here, where the second-level belief is different: not that believers are morally superior, or believers go to heaven, but that believers are cool.