Is the 660/12 the only 12-string model with a wider neck width at the nut?

Nope, there's also the 1993 Plus. It's in the Models section under the 300 series.

1993Pus is a great guitar! I do not know why they would not make the wider neck for the standard 360/12 Ric. It just makes good business sense. But so far "No Dice"! At least you have the 660 and 1993Plus options, but I'm not getting any younger, and my hopes are fading away for this models(360/12) wider neck!

Just speculation on my part, but I'm wondering if the narrower neck and closely spaced strings on most Ric 12 strings do make a difference in the sound? I've never played a Ric 12 string with the wider neck, so I don't know for sure. But playing my Ric 330/12 versus my acoustic 12 string with a considerably wider neck, there does seem to be a difference and I don't think it's only due to the reverse octave string arrangement on the Ric.

It sounds to me like there is a more harmonic sitar-like drone effect on the Ric due to the more closely spaced strings sympathetically vibrating and even slapping against each other. Or is that just my imagination?

I don't know if that had anything to do with the decision to go with a narrower neck on most Rics. Most likely, it was just simple cost savings by using the same neck for both 6 and 12 string models. I think like many Ric 12 string players, I can live with the narrow neck since I have fairly small fingers. But I would probably prefer the wider neck if it was available on more models.

For years I've been saying that ALL the 12 string models should have the wider nut width, and 99.9% of ALL Ric 12 string guys would prefer the wide neck, AND, Rickenbacker would sell MORE guitars to the guys who already have the narrow neck 12, AND sell more guitars to NEW Ric fans who DO NOT play Rickenbackers because the neck is too narrow, but love the sound and look of a Rickenbacker guitar!!!

I have one of the 3 650s that were converted to a 12. So you have the wider neck, but also cool maple board, and bigger frets.

Sorry to disagree with my Rickenbrothers, but I don't see any reason for a wider neck on the 360 or other models. And like everyone else here, my fingers are much fatter than when I bought my Rick 12-string 40 years ago.

A few years ago, I bought a custom-built six-string with a wide, flat fretboard and I loved it for string-bending. But my old 360/12 plays much easier and faster, especially for sliding chords way up and down the scale. It has always been the fastest and easiest guitar I've ever played, except for a 381 I tried out once.

Since Rickenbacker now offers a 1993Plus and the 660 models, any urge to play a more spacious hollow- or solid-body guitar should be well satisfied.

Well you and Mr. Hall seem to be on the same page, but the majority of us are not!
The wide neck should be standard on all 12 string Rics, and if you like the narrow neck, well there are plenty of them for sale because even Ric lovers eventually sell them for a more comfortable playing, wider neck!

Well for those of you that are interested I looked into the nut widths on my guitar collection.
Rickenbacker 660/6 2011 44.5mm
Fender Elite Telecaster Thinline 2018 43.8mm
Gibson LP Studio 2019. 43.053 mm
Rickenbacker 330/6 2009. 41.4mm

Makes interesting reading and they all play nice but my favourite is the Rickenbacker 660/6

It seems that some of the Rickenbacker mystique comes from the original neck shape and width, at least for the 6-strings. The 12-strings have been a controversial issue to say the least. I don't think RIC should widen the necks on every model, but the 660/12 & 1993 are definite improvements.