When a
sound reinforcement system is involved, coincident mics are imperative,
since spacing the mics generates very unnatural correlated differentials
from the separated sound sources putting out the same signal. When you
have
a broad ensemble of acoustic sources, you end up somewhere in between.

But why would one be doing stereo with sound reinforcement?
The few times I've tried it the variation due to position
in the audience has made it useless unless you are really
close to center and even then it just doesn't come out right.

"Close to the center" indeed, within a few mm of exactly dead center so each
speaker is equidistant. Even with a mono mix, I've gotten vivid stereo
results with a Rode NT4 in a rear position, widening the crap out of it in
post. Widening such a narrow field of direct sound to offer some off-center
detail from stage bleed, the room ambience is wrapped all around. What you
end up with is the best of both worlds - the PA detail of a rear position
and the impact and imaging of the front row. You really have to nail the
mic position though, and any time differentials from mic spacing are
unacceptable, even the dual card's in the typical SDC fig-8. The slightest
inequity in the front/back response of a single diaphram fig-8 would be
grossly evident as well.

For that particular purpose the NT4 is the go-to mic. For loud shows you
can pop a 9V in the chassis and use the included minijack cable directly
into the line input of a NJB3, and for ~$600 total the results are
freakishly good.