Small room acoustics is nasty in the bass region and due to the limited position of the monitors/subwoofer I was certain that some kind of EQ was needed for my new 2.1 desktop system. I thought the dip-switches most likely would not satisfy me.
As for diminishing returns, it's for me about features and performance that I need want, and in this case it made sense for me even though it was more expensive. For me, personally, a pair of 8331A while nice could not compete with a pair of 8330A, the 7360A subwoofer, the GLM Kit, cables and money leftover.