Nothing about Data's design is trivial. Sure, the positronic brain was his utmost preoccupation, but that's only because he had so much trouble with it, & faced pretty much everyone telling him it wouldn't work, but everything about Data's design is a fantastic achievement, even more so for Juliana Soong, who was nearly indistinguishable from a human. They all marvel at the complexity of design, that's intention was to create a machine that mimicked our own as much as possible. His goal was to create an artificial humanoid, & yes, the most complex part of that was to create its mind I mean why would he make the thing capable of dreaming? What need does a computer have for dreaming, except for it to live as we do?