Do larger planar speakers produce more accurate sound?

If not married to planar, maybe you should consider Magico.

If by “clarity” you mean an absence of resonance that makes for a murky or muddled sound, panels and compression midrange drivers can be very good.  The very best compression drivers, such as those made by Western Electric, International Projector Company, YL, G.I.P., Goto, manage to substantially avoid nasal resonance that color some compression drivers and deliver clear, detailed and well textured sound with a sense of ease.  These drivers must be matched to very nimble and clear sounding woofers.  The woofers that seem to work best have light cones, and pleated paper surrounds.  The downside to such woofers is a limited excursion that mean they don’t deliver extremely deep bass.  This kind of bass is similar to that of large panel speakers which also don’t go extremely deep.   

Larger speakers play louder, but the Magnepan LRS is really a remarkable speaker and its accuracy is quite high, in my opinion. I am a musician (guitar, mandolin, uke) and regularly play five time per month with a group. My experience is with 3 models of Maggies, and a friend has some Martin Logans. I have built may and use open baffle speakers in my big system. Large doesn't necessarily mean more accurate.

I do not know if they do or not, but I really like my Maggies MGIIIa.  I enjoy the sound much more than box speakers.  I really do not care about deep strong bass; the Maggies produce nice clean bass and enough for me.

No one has mentioned line array (open baffle or not) speakers. I have only read about them, but I wonder if they might address the OP's call for "clarity" or "accuracy" or whatever magic word equates to what he wants.