Yes, dipoles, particularly panel type dipoles can make a significant difference in sound levels outside of the sweet spot. In addition to the cancellation effect mentioned above, panel dipoles, with their large radiating surface have a number of other advantages. First, they are less like point radiators and more like a line radiator, so sound level does not fall off as rapidly with distance from the speaker. Second, line radiators have poor dispersion in the up and down direction which, again, concentrates the sound at the listening area and reduces energy elsewhere.
While I have noticed this effect with the two panel dipoles I have owned, the Martin Logan Quest and Acoustat 1+1, I have not specifically looked at this quality with other dipoles. Based purely on sound quality, I like the Magnepan 1.7 for an apartment setup--it is small for a panel, has reduced bass output (bass is the main problem with sound transmission into the structure of a building). Various Quad electrostatic speakers are also very good, not only for their dipole dispersion but because they sound very good at lower listening levels. If you can find an old Quad 57 in good working order, that is a terrific apartment speaker.
Outside of the dipole realm, there are certain speakers that are very enjoyable at surprisingly low volume levels. The best in this regard, are horn systems, but, good examples of these can be very expensive and bulky. But, there are other speakers worth looking into for lower volume listening, such as the smaller Audionote, Proac, DeVore, Spendor and Harbeth speakers.
