Based on my measurements of a few rooms and many sets of speakers (with a calibrated mic to +-1DB), a very average, unprepared household room, with only basic effort for placement and sweet spots can easily contribute to far more significant inaccuracies in sound reproduction that the cheapest hi fi separates available, at least 75%.
From tweaking placement, toe in, adjusting crossovers (both active and passive) I am often able to able to flatten out peaks and troughs by atleast 10DB, then we rapidly hit laws of diminishing returns (in terms of cost) for improving the room/environment and at a point where spend more on your hifi equipment will be beneficial also.
I've helped setup for a few small live gigs too, really learnt to appreciate parametric eqs and notch filters !