The room is the limiting factor in most speaker setups. The worse the room, the sooner you hit diminishing returns for upgrading any other part of the system.

In a fantastic room a $50 speaker will be nowhere near 95% of the performance of a mastering monitor, no matter how much EQ you put on it. In the average living room with less than ideal speaker and listening position placement there will still be a difference, but it will be much less apparent due to the limitations of the listening environment.