Should a reference speaker be neutral, or just great sounding?

Erik, "reference" is just a marketing term. Marketing should mean absolutely nothing to everyone. 
With enough experience and technical information, along with knowing what one likes to listen to, you can evaluate a speaker based on it's design and specification. If it rings all the right bells then a good listen is in order. There is no place in this country I would not fly to to hear a speaker I was going to pay more than 20 grand for, less if the dealer was say within a 250 mile range.

Good point, Eric....getting lost in the semantics is but one lurch towards commentary chaos....+1

Mho.....(among others.....*G*)

Neutral > If I was to run a tone sweep through Spkr A, the trace on the waterfall RTA will match up to what my equipment (calibrated mic, all that..) will depict as close as possible, given as silent a test space as possible.  Any gross deviations become obvious...

Reference > As previously noted here, usually applied as 'hype' for the new 'type' of Spkr Z.  Unless one applies the previous routine to Z with favorable results, it just calls attention to Company Z's new 'high water mark' for their offerings.....

Now....I don't have any real favorites with regards to any particular brand or mfr.  I've heard/listened to various 'n sundry in v. 'n s. situations, locations; some have strengths, others with weaknesses, and then the ones you walk right by for whatever reason/rationale.

It's all subjective in the end....what fills your ears in 'That' way....and can be rationally afforded in whatever matter/means.

A personal observation that y'all can either have a laugh/jeer/contemplation over....

I'm 'away' from my personal space periodically.  This can be for a week; sometimes a month or three.  I have in that interval just the memory of that which I've left behind.

The longer the interval, the more my speakers may sound 'alien' to my ears, a certain familiarity has lapsed to varying degrees...

It may take a day or two to 'recover/revive' that acknowledgement of 'OK, nothing's the matter or wrong.....it's just Me.'

The psyc of sound, if you will. *G*  Anyone else have this experience?

A neutral speaker can still be sluggish or intransparent. ‘Great sound’ encompasses lots of things, especially the owners preferences.
A truly reference speaker in my mind should have neutrality, speed and transparency to properly sound stage, image note decay and allow for tuning through positioning. In my experience neutrality, speed and transparency are vectors on which people in comparisons tend to agree.

If you set up Magneplaners correctly, they reproduce what you send them.

If that is your idea of "reference" then so be it.

Try playing a musical instrument live--a piano, possibly, as they are somewhat difficult to record--and then play the recorded version.

If you don't hear any difference, either your ears are not trained or you have a pretty good system, I would say.

That's what Maggies do if your system is not weak in some area.

Try it and see for yourself, of course.  Don't take anyone's word for anything.

Cheers!