We should reject hard-to-drive speakers more often

That does indeed read like a good bet Ralph.  

Don't know how to explain it; driving our North Creek crossovered B&W Matrix 801 S2 speakers (87dB sensitivity, nominal 6 Ohm with benign phase angles and amplitudes) with only our 100 watt monoblocks (2x6BL7 + 4xKT77) sounds both better...and louder!...than driving the woofers with a Jon Soderberg modified Threshold Stasis 2 (~225 watt/ch.) and the tube amps driving the midrange and tweeters. 

I chalk it up to coherence tricking my brain into thinking it's louder...are there decibel meter apps for smart phones?  No need for responses to that...Google here I come.

Having recently place the Vandersteen Sevens in our Listening Room.  83.5db.  Never would have thought to pair them up with a SET 28wpc stereo amp but there you go, drove the hell out of them.  So you need to try things in order to find what will work in your system.

Happy Listening.

@ bigkidz +1

The theory doesn't always hold true.

I drive my W/P5.1 with Pioneer M-22 2×30 Watt A-Class, sounds amazing.

Speaker designers are driven by their education, experience, practice, and their personal sense of hearing, and they're sometimes also biased by what they or their marketing partners believe is consumer preference at a certain price point. How each speaker designer arrives at his product goal creates a whole variety of synergies, dependencies, and sound profiles. None of those resulting designs are wrong or hard to drive unless the home audio consumer market stays away from the product or the reviewers kill it.

Basically today, there is so much speaker choice in the marketplace at literally all price points that something perceptibly hard to drive is essentially a side issue because there are always identically excellent choices that are ideally suited to someone's existing amplification and room and physical cabinet size preferences. 

Suggesting that "hard to drive" is a no-no implies that development decisions by speaker designers should be limited. I think that's counter-productive.