I do think full range drivers have merit and are interesting. I quite like the simplicity, cost, and elegance of single driver speakers using a pair of sub $300 Fostex drivers for example. I lose interest in audio gear when products whether speakers, amplifiers or dacs feel unnecessarily complex or overbuilt.
I've achieved excellent sound from an FE206EN with a ribbon tweeter in a small BLH type enclosure. Though other speakers are perhaps more suited for complex music at medium volume as was my experience. I attribute this in part to the Fostex driver reaching its mechanical limit and compressing under said circumstances. The consensus seems to be that Alnico motors are better suited for single driver applications than ceramic magnets due to "smooth compression" of the voice coil. Here's an explanation a member from another forum posted:
"The whole 'Alnico mojo' is about smooth compression at high average levels, such as what you would have running the amp flat out. AlNiCo (Aluminum-Nickel-Cobalt) is an alloy magnet and all alloy magnets are easier to demagnetize than comparable Ceramic (Strontium Ferrite) magnets. What this means is that as the voice coil starts moving in response to the input signal, it generates a magnetic field of its own that tries to demagnetize the magnet. As its effect lowers the available magnetic field of the AlNiCo magnet, the speaker becomes less efficient, the voice coil moves less, etc. The physics of it is that the small magnets near the surface of the magnet poles (called 'domains') begin to change state, or flip directions. The result is smooth compression, the same kind of operating curve compression that occurs in a tube amplifier. The ceramic magnet, on the other hand, doesn't compress or demagnetize as easily, so the voice coil moves to its mechanical limit and won't go any farther. This is why some players say ceramics sound a little edgy at high average levels as opposed to AlNiCo. However, by properly designing the entire magnetic circuit, ceramics can be made to behave quite well for desireable guitar amp tone and dynamics. You might compare the two magnetic circuits to solid state amps versus tube amps, where the solid state amp gives it all its got then clips hard, while a tube amp compresses nice and smooth. The extension of this idea, then, is that with the AlNiCo, like the tube amp, you can seem to have a louder average volume since it gets compressed smoothly. By the way, the compressing or demagnetization that occurs with the AlNiCo is not permanent. It springs right back to its design operating point."
A voice coil is like an electric motor. The bigger the voice coil, the more wire used, the more torque or pulling power you have to move the cone. With the proper match of components, you can get more sensitivity, wider frequency response, and more power handling ability."
Hence the mega Alnico drivers by the likes of Voxativ, Feastrex, etc. In addition, I've heard much praise about, though never heard the Seas Exotic 8" Alnico driver. The most desirable of the aforementioned TAD drivers feature Alnico magnets.
I think full range (very low mass) drivers can be excellent in two or three way systems. Here's an example:
http://lampizator.eu/SPEAKERS/PROJECTS/P24/P24_monster_speakers_raal_altec_lansing.html. The Lampizator guy has apparently DIY'd tons of speaker systems over the years, including a system with those mega magnet ATC midrange domes, and seemingly settled on this design, featuring some very lightweight SABA Greencone drivers with Alnico magnets, and large Alnico bass and subwoofer drivers. This seems like a nice and fairly cost effective setup.
Complex DSP, waveguide and coaxial implementations aside, dipolar speakers like the Pure Audio Project speakers with the right components, are the preferable speaker design in my opinion.