S.G. cannot do the impossible and give to us a natural musical timbre accuracy for example.... They can contribute like ionizers do...
But natural timbre accuracy PERCEPTION dont come DIRECTLY only FROM the speakers design either ....I suppose for sure we speak here about any relatively good speakers and for sure their design play a critical role...
But natural timbre accuracy PERCEPTION or experience come DIRECTLY FROM the room acoustical settings contributions...
And no S.G. or ionizers could replaced, only by itself, passive materials acoustical treatment and certainly not more active (non electronical) controls like Helmholtz grid....
Then yes S.G. are cheap and audible positively for many who will bought them....
But there exist no miracles in Acoustic....Only laws....Complex one...
The main criteria to know for sure if your system is accurate and high fi is not soundstage or imaging "per se", it is natural instrumental TIMBRE tonal accuracy perception...
Here the room acoustical settings are critical in the process of making possible the recreation of the Timbre instrument "envelope" perception ... No turntable or dac can give it by ONLY itself.... It is the room acoustical synergy settings controls with the speakers which is the key... S.G. are only a small contribution...Like ionizers... Like many others ....
The more powerful are passive materials treatment with the right balance with absorbtion/reflection/diffusions surfaces and volumes...And activation of the room with Helmholtz pipes and tubes or bottles... Secondary more passive resonators could also give something...
Then wait for a possible pleasant surprize with cheap S.G. but not for miracles and in some case if the noise level is too high no audible effects....