Smaller bass drivers have gained in popularity for two reasons.
A) They allow the speaker designer to make the speakers smaller, so they usually "image" better.
B) they may not go quite as deep, but the bass will be tighter.
AFAIK, Sensitivity has nothing to do with the sound being "fuller". Yes, you may need to turn your amp up a bit more for less sensitive speaker to play at the same sound level, but whatever listening level you are at, 80 db, 85 db, is still 80 or 85 db no matter what the sensitivity rating of the speaker is.
A) They allow the speaker designer to make the speakers smaller, so they usually "image" better.
B) they may not go quite as deep, but the bass will be tighter.
AFAIK, Sensitivity has nothing to do with the sound being "fuller". Yes, you may need to turn your amp up a bit more for less sensitive speaker to play at the same sound level, but whatever listening level you are at, 80 db, 85 db, is still 80 or 85 db no matter what the sensitivity rating of the speaker is.