so many speakers

"If the answer (or consensus) is "NO," then how can one in the market for new speakers make an intelligent and informed decision?"

There is NO CONSENSUS concerning ANYTHING on this site. Ask ANY question about ANYTHING and you will see. You cannot use the posts / answers on this site as factual evidence about anything!! It's a big waste of time to try. Find speakers you might like based on size, cost, looks and specs and listen to them. If you like them, case closed, Phase angle and crossovers and impedence notwithstanding. Can you hear phase angle? We as a species can barely hear a full grown male lion coming thru the grass. All of our senses suck! Get what you like and be done. For every person that says buy A, there will be just as many saying buy B, and a few saying buy Z.
And nothing you asked has anything to do with technical expertise. If all 'opinion'. And trust me, EVERYONE here has one of those.
Cheers.

Surely there's a consensus that there are audible differences among speakers!

Rok2id, yes . . . I agree with your take on the subject. Let me just add that there is a thread out there that pops up from time to time which asks what are the best speakers on the market, or something to that effect. At last count, there were over 1300 hits on that thread.

As I see it, if the consensus view is that it is NOT always possible to compare two speakers, even under identical test conditions because of synergy issues with the rest of the system, the amp in particular, are there any guidelines that one can look to when trying to make an informed decision.

I make this point, because as a general matter, it's generally not practical to bring one's amp to the dealer (least of all the rest of your rig). And even if one does, many dealers wire up their test gear "behind a wall" for aesthetic reasons, thereby making it difficult to tie one's amp into the dealer's system. Hence, how can one make an informed judgment, even relying on your ears at the dealer's showroom?

What sounds wonderful at the dealer, could very well suck when you bring it home. Then what are you going to do?? Try to exchange out your speakers, or just live with them, or start the A'gon merry-go-round??

That's why I posed my Q. IMHO, to ask for speaker recommendations in a vacuum is silly. To respond to such questions is even sillier.

"Surely there's a consensus that there are audible differences among speakers!"

Yes, there can be differences. But, I think there are fewer differences than we might think. If we could really test them, we would find that there are 'groups' of speakers that are sonically the same. In other words, my Polks could end up in the same group as the Wilson Maxx. :)

So, of ALL the speakers on the market, we could end up with just a few different groups. Some people think, believe it or not, that speakers are the ONLY component that exhibit differences. :)
Cheers.

Do you want to listen to your hi-fi or listen to the music?

When you have decided which it is, then we can move on.