They would disperse more sound, no doubt, but only if you're listening to background music would it be worthwhile.

Watching a movie would really sound bizarre with two sets of mains, or listening carefully to a CD would have no more stereo imaging and soundstage.

If you have a 5.1 system, try listening to music in 5 channel stereo to see if that satisfies you before buying more speakers, which leads to buying more cables and probably more amp power to feed the new ones!