dots cluster
The clustering of the points about (2,4) might make you suspicious that
there is, indeed, spatial autocorrelation. We don't have enough points to
actually hope to model it, but it appears that it exists. It might be smart
to just assume the simplest model, a linear model, and estimate the value at
3 at about 3 (linear regression would get you about the same answer).
Taking a mean in the face of spatial autocorrelation here would not
be smart: you'd get a value of around 4, when it appears that the region
around 2 was heavily oversampled. IDW (Inverse Distance Weighting) is just
as bad an idea as taking a mean. The problem is the same: you'll overweight
the region around 2.
A sensible variogram model used in kriging will downweight the
cluster, and would produce a value of around 3.