[face of glass]

Sharon, I don't know if you started this because you want to continue our ridiculous Buckingham vs. Nicks debate or not.
I even have my reasons to doubt McLoone's comment, since fans have generally assumed that it's Lindsey who's responsible of the sigh in the middle of the "I wanna be a star...I don't wanna be a cleaning lady" statement.
But let's assume that Annie McLoone is right, that Lindsey didn't contribute anything else than the sigh to the demo.

This is a surprising I must say. For sure the record version is better but all the elements that make Sara brilliant are pretty much there on the demo and if what they say is true it sounds like Lindsey wasn't on the demo at all.

I don't understand what's so surprising or even shocking about this "revelation".
We all know that it's Stevie playing the piano riff, her own invention, a thing that wasn't changed in the finished product (as McLooney stated, they used the demo take on the album and for me they've always sounded like the same thing anyway). And her vocal delivery didn't change that much either.
I've always believed personally that Mick didn't need that much guidance in what he played for Fleetwood Mac.
Moncrieff pretty much maps out the territory for John's bass, although he doesn't have the same feel of flexibility that John has. And I think what I said above of Mick can be said of John too.
Since you think I'm nothing but a generic Lindsey fanboy I'll switch to that mode for the following.
Personally I find "Sara" a good song, not necessarily technically but it can be seen as moving, for sure. Even then, nine minutes of the demo is too much for me. I think it is a monotonous, plodding piece of music that for me works as a background thing but when I actually try to listen to it I get bored by it somewhat. The demo is a thing that hardly makes any distinction between the verses and the choruses; it sounds like a very undynamic thing overall. I don't think I would enjoy it more if it was cut down to the length it is on the album (or to the four-and-a-half minute thing that it is on the original Tusk cd).
I like McLoone's experiments with her background vocals but overall they don't add up for me. And Moncrieff, in the end, mainly supplies rhythmic work, the territory that Mick and Stevie are already working in with their respective instrumental parts.
Obviously when Stevie gave Fleetwood Mac a mid-tempo song in the '70s Lindsey sometimes felt compelled to add various vocal harmonies to the songs, along with his own lead guitar. That's how "Dreams" works, and similar ideas are explored further in "Sara" (and later they will find their way to "Gypsy").
Now the demo hardly moves me. I'm not one of those fans who grieve over a lost Stevie lyric and I'm certainly not longing after the legendary 16 minute version of the song. It would have just had more stanzas in it, nothing more.
The album version brings me to tears, sends shivers up and down my spine and turns me into a raving fanatic, someone who should not appear in public for a while.
But it doesn't mean that I can't do my "cold and pseudo-rational" analysis of it as well.
I find the album version much more dynamic than whatever the demo offers us. A huge part of that is due to that incredible harmonic background that enters the soundscape the first time after 1:30 (and the second time after 3:30); it is that thing that gives the song an artificial (but very functional) separation between the verses and the choruses.
The harmonies make the song sound like it's distant angelic singing over our heads, a darn complex (but never too esoteric) thing that contrasts with Stevie's raw vocal and the amateurish piano playing, thus giving the song even more charm. One thing that especially makes my heart sink is the inclusion of those descending harmonies from 2:13 onwards; at that point I'm just shivering.
I also think it was very clever to use two unidentical piano tracks in the final product (in different channels, I'm not referring to the lower bass notes but to the bulk of the riff); it gives the rhythmic backing variety and prevents it from becoming too monotonous.

Basically I do not see this thing as anything else than this: if you love Stevie Nicks' lyrics and her songwriting, if you love her delivery and if you have no general problem with the monotone demo and hear all the subtleties in her voice and that is enough to get you by, fine. Then you will probably think that "Sara" the demo is pretty similar to the album version and that's that.
But if you want diversity to the proceedings, are not missing the lost lyrics and want the thing to achieve a lot more musically in its six minutes then the final Tusk album version will most likely take the cake.

And even then there's still something that makes the tune a classic melangé of Buckingham and Nicks; Lindsey's guitar tracks.

I'm constantly amazed at what he plays in there; it sounds similar at first, yes, but there's such an amount of care, emotion and subtlety put into those tracks that I can't help but be as moved by those as I am by Stevie's delivery.
It's pretty much what another Sharon said of Lindsey's and Stevie's musical connection; it's like their personal styles are merging together on paper. In this case the guitar goes where the voice can not go, it reaches out for that same divine emotion along with the voice and drives them both to their best performances.
Even if Stevie did her final vocal take for the song before Lindsey added his guitar overdubs the guitars still amplify Stevie's delivery and message even further. For me it validates my point of the special relationship between Buckingham and Nicks; if there's someone willing to give his/her all for the song then it comes through in their playing and influences the other as well. And there's no way they would give out such performances if the other wasn't there. This is a thing that a Stevie solo record never has; there's never a player in there who would speak to Stevie in such a way.

The whole tone, the atmosphere of the song just changes in the final take when you compare it to the demo.

*steps out of the fanboy/SNL shipper mode for a while*

Even then, while people may claim that the song itself wasn't transformed when Lindsey got his hands on it, it still doesn't prove that it would have been a success in its demo form (or if Jimmy Iovine had called in some players to add mild overdubs to it, for instance).
The thing that was the single chart hit, and is still played in the American radio today, is the Fleetwood Mac version. And my belief is that the demo wouldn't have been successful at the time. Even Stevie herself seemed to feel that it wasn't fit for release as such. Grieve over the missing lyrics if you want to, but the prolonged version would most likely have driven a lot of public away from the track.
And those who claim otherwise seem to me to be nothing more than people who listen to Stevie Nicks' lyrics and performance (and the basic songwriting) first and then to the rest. And there's no way to tell what the general public listens to in a particular song.

Thank you, Sharon, for making me listen to the song again though. It had been too long a while. And I also noticed someone speaking in the left headphone after 5:25 or so. Can anyone hear what is being said there? Are they satanic backwards messages?