I'm with Nick D on this one -- I have yet to hear a good surround setup.
Wait, that's not true. I went to a concert by James Dashow. Most of his works are of the "Variations/Inventions/Tone Poems/etc. for ____ and Computer Generated Tape". He generates the tape from a computer using, basically, FM. He usually does it for four channel. I heard everything. I heard sounds scurrying around. I heard an entire diffuse cloud of sound coming from everywhere at once. I heard a single monochromatic tone coming from what appeared to be the center of my head.
But that was a long time ago (in the mid 80's), and since the advent of surround sound, I have yet to hear such attention paid, not just to the colorations introduced by speakers, and their consistency, but to phase, which was key in Dashow's "performances".
And I doubt I ever will. Most of the music I listen to is rock, which is inheritly non-audiophile. Most of it is produced in ProTools with little or no attention paid to this so-called "soundstage". Sure, they pay attention to frequency spectrum and blacker digital blacks, etc., but not to soundstage. These guys (the ones I listen to, mostly) would be the ones whirling electric pianos in circles around your head, buzzing you with airplanes, spreading birds and bugs and bees in a panorama of (surround) sounds, but, other than maybe a remaster of the Cowboy Junkies album, The Trinity Sessions, or some other such exceptional stalwart of true sonic reproductionism, no soundstage.
So I'll stick with two-channel. I have a cheap HT setup in the next room for the occasional novelty, but for the most part, two is good enough for me.
So, in answer to the original question (is it a gimmick), no, at it's very root, it is not, but it will be treated like one, and I will treat those clowns with the respect they deserve.