Low-sensitivity speakers — What's special about them?

+1 tomic601.  I have installed a  pair of Vandersteen Model 3 Subwoofers.  They are sublime.

What it comes down to is... really good mids with any type of top end extension without cone break up is hard to find in true high sensitivity speakers.  It has already been mentioned about bass.... The bigger the magnet/motor structure of a woofer, the more sensitivity and the more mass it needs to produce low fs/Qts.... these are attributes that lead to deep bass.  As you as you ad mass fs goes down and qts goes up,  but the trade off is that sensitivity goes down.  
Its not a perfect world.  I try to find the sum of parts as a whole to start the design process. Not being able to find any single part can kill an entire speaker project.  
Alot of people really like sealed box speakers for bass, I am one of them, but woofers that work well in a sealed box need a qts of a minimum of .4 and preferably .5 or even a bit higher.... Look at spec's on high sensitivity woofers,  you'll see .2 to .35.  This is just too low to produce bass in a sealed box system,  Although .35 can produce very satisfying bass in a ported or vented design.  You also have to consider that most good designers prefer to keep the crossover out of the vocal range,  so again,  it requires drivers with a fair amount of extension on the top end or bottom to pair with other drivers. 
There are plenty of excellent parts to design high quality low to medium sensitivity 2 or 3 way systems with great results. 

Every speaker, to some extent, makes some trade offs, and, at all price points, imo. The thing is, as a listener, we need to determine, what musical parameters of recorded music, are most desirable to each of us. And as explained above, the speaker / amp / room combination, should be matched as close as possible, to work together. Someone above, although appreciating the efficiency of horns, prefers other things. I, on the other hand, prefer horns, and the efficiency, is simply, icing on the cake. Advice : Take you time, and listen to as much gear as you can. Also, go listen to some live, " un-amplified " music, as this will give you an indication, as what to listen for, in audio gear ( speakers, specifically ). My best, and Enjoy ! MrD.

I’ve always gravitated to lower sensitivity speakers mainly because they were the speakers I enjoyed the most. Pluses and minuses either way I suppose. Dynaudio makes excellent speakers if you buy the Evokes I bet you would be quite happy. Down the road you could consider the opposite and drive a highly sensitive speaker with a low wattage tube amp, that is what makes this hobby fun.
Right now I am enjoying Magnepan LRS speakers that are quite different from box speakers. Could I go back to Dynaudio or Totem someday - probably. Anyway my point is buy what sounds good to you, no matter what you buy you’ll have to match it up with proper amps / stands / Dac anyway so don’t sweat it. 

The advice to get speakers that I enjoy and then find the amps to match is how I was initially going forward.  It was the warning that I might be boxing myself in that caused me to reconsider the speakers that I had heard and enjoyed. But there are more speakers out there and some of them might be higher efficiency...so there’s no harm in just doing more listening! Of course if some delightful and expensive tube amplifiers really make a big difference to the sound, well, then, it might not hurt to consider that as a potential orienting factor for the speakers! You see how I get turned around and around! Still, it makes sense to start with the speakers.