Soapstone, yes...I find that the denser and heavier the body, the tighter the low end. Even the ad vox which is quite lacking in tightness of sound feels a lot tighter with this.
I don't really much believe in body resonance having a big effect on electric guitar sound at all, its more bout the solidity. too lax and soft wood or plywood etc. are bad, but most any solid material does quite well in bodies. Make a body out of car suspension parts or other iron pieces and even that works ok.
BUT Yeh, soapstone does make for a good heavy rock guitar...tight!