Relative importance values are entirely impressionistic and not based on any rigorous study. The multiplicity of possibilities is partly due to the fact that plural marking is optional.
As for value 2, I have not found any examples of bare singular nouns outside songs and proverbial expressions.
Source: Smith 1974-5: 5188
Source: Smith 1977: 148-149
Source: Smith 1974-5: 5345