If not, can they add any info to our understanding of our world?
who said their existence can be explained only on the basis of whether or not they add to our understanding?
Hashem works in many complex ways and through a complex spiritual and physical system of many intermediaries (see Derech Hashem)
every blade of grass has a malach associated with it. millions of malachim sing Shira every day. does this enhance our understanding of the world?
i dont know why there are sdim, but i have no intention of disbelieving the Gemorah and Midrashim, and Seforim because i dont think it makes sense