> have become two of the most valuable references in existence

Well I'm not sure about that. Wikipedia is the better of the two, but that's a low bar. Articles are poorly written, inconsistent, and targeted at wildly variable levels of existing knowledge. I rarely use it for anything other quick lookups of trivial facts (and even then only for unimportant purposes). It's much-visited, but that's an indicator only of ubiquitous availability. I remember long ago reading some study or other comparing its quality favourably to old-fashioned encyclopedias, but it was just a fairly risible surface fact-checking operation. Of course Wikipedia is huge so there may be vast areas of excellent quality unrelated to my interests.

SO is worse, but a little more useful because of its narrower scope.

So, no, IMO toxicity of community and quality of output aren't related (in either direction).