Brownsfan, your worries are over....
I auditioned the 1.7s and 3.7s at the time of their release. The 3.7 was particularly of interest. I took my wife along to the dealership for a second opinion. Using my own Curved Air CD I felt Sonya's voice was made to sound quite ordinary to the point where it was severely lacking in content(!) Much of the seductiveness of her voice is embedded in the lower octaves and it was posted missing here. My words to the OH at the time were "it made Sonya sound like a bad singer that you wouldn't give a second listen to" - which she obviously isn't.
Back home I rechecked against my Martin Logan Vantages and the difference was night & day. The sense of relief was palpable. On the basis of that comparison I wouldn't touch the 3.7s with a barge pole.
Fast forward to a few weeks ago and an audition of the 3.7i.
I didn't have the Curved Air test pieces but the dealer provided some Joni Mitchell instead. Having been privy to all the recent discussion about secret crossover changes I wasn't expecting a massive improvement but was shocked to find that they'd managed to significantly address the bass problem. ("How'd they manage to do that with a crossover update?", was my first thought). Joni's voice sounded perfect. She was fully corporealised standing 6ft tall in front of me with all registers of her voice perfectly rendered and convincingly better than my recollections of the "old" 3.7.
I double checked with some ELP to see how it handled the heavier stuff and while they would never convince the "bass-heads" among us I was stunned by the sheer coherence of the musical presentation and the level of detail. Little things popped out of the mix that you'd never noticed before.
The bottom line is that although I wouldn't have touched the old 3.7 with a barge pole I WOULD buy the 3.7i in a heartbeat. That's the important difference and it bypasses any hifi technobabble that I or anyone else might offer.
Since then I've become aware of the ribbon tensioning updates and it all becomes clear.
The question is, was the 3.7 a mistake that needed to be rectified?? (..and more importantly, should the punters be paying for it?)
Furthermore does the difference in the manufacturing justify an extra $500 when they'd already, apparently, adapted their manufacturing process to release some of them as 3.7i under the guise of 3.7s? (and did those people pay $5500 for them?)
Alternatively, how loose can the 3.7 panels get by mere playing? Will they ever match the 3.7i when fully run in?
Not that I would ever accuse Magnepan of being underhand because they've always been fair with their customers but I think the veil of secrecy needs to be lifted a little to reassure the customer of the necessity to shell out the extra $500 at the very least?
Meanwhile I'm still drooling over them.... :)