Would you buy a pair of speakers by just looking at the measured freq. response?

No.

No.

Off-axis response, impulse response, dynamic range, distortion, all matter. 

I also have to say that, by the same token, I wouldn't buy a subwoofer and configure it based on published specs either.  The speaker in the room is a very different beast than the speaker in the lab.

Maybe add a little. I’ve come to learn that certain reviewers like a ragged response in the tweeter. I do not. Mind you, I did not first look at the response and hten decide what to like, I really disliked two speakers I had listened to in person for having a treble response I found unlistenable, then I read the reviews with measurements and went AHA!!

That ragged, up and down response between 3 to 10khz really bugged me, but the (very important and famous) reviewers praised both these makers for the same reasons, calling one a poor man’s version of the other. Ugh.

Also, a speaker like modern Dali, many models have stepped up mid-tweeter response. I can hear it and you can see it in the plots.  BTW, this design has it's uses I just am not looking for that.

So, while I would never buy based on measurements I’d probably avoid a few based on them.

If measured well that would absolutely influence my buying decision all other things aside because I have been around enough to take that info for what it’s worth but buying any speakers without hearing first is risky business. If you do it buy used so can resell or buy with a suitable return policy only.  Otherwise be willing to take a financial hit especially for pricey high end items.  

Use the frequency response graph as a preliminary filter (kind of like tossing away candidates that didn’t go to college when reviewing résumés), but don’t ever buy speakers from a store or seller that doesn’t have a decent return policy and/or allow at-home auditioning of equipment because the room you set the speakers up in is equally important as the natural response curve of the speakers because the acoustics of the room will heavily dictate which speakers work out for you and which ones won’t.

-Ed

PS On a related, but separate note, I wouldn’t really hesitate to rely heavily on a frequency response curve if researching in-ear-monitors or headphones. Totally different situation there, and part of why I consider headphones a lot easier to pin down.