Naturally. The door tells us explicitly what TPTB wanted: "something new". This defines the end result: "a shuttle the audience will consider a new addition to the Trek universe".On the entire design, the door is literally the ONLY difference in the entire design; this, to you, is the "only thing of any significance?"
After all, the door is not merely the only "difference", it is also the only feature whatsoever on the existing prop! Its significance thus is basically infinite.

Whether the shuttle is intended to be a 2250s evolution of the 2230s shuttle or not is irrelevant. It's only your original and baseless conviction that TPTB "attempted" to recreate the 2230s shuttle that I find so absurd. If the shuttle we see is a 2250s modification, then your conviction is wrong - TPTB did not "attempt" to build or perhaps rebuild Robau's shuttle and tragically fail.
Mistakes on both sides... Yes, it's a miniature, but no, it doesn't have Type-6 nacelles - it has the old ST5 ones.No, the TFF shuttle prop was actually rebuilt into the Type-6 shuttle for TNG. The design we saw in Generations was a miniature and no full-sized prop was ever built. The miniatures used in Generations preserved the new nacelles and window arrangement that were present on the Type-6
The point is still valid: they used existing material to create new material, but the dramatic intent wasn't to reproduce existing material - it was to create new on the cheap. And that's the only thing about your assertions that I object to: that there would have been an intent to recreate Robau's shuttle, rather than merely use possible available material to new purposes.
Umm, you sure?As no exterior set piece was actually built for the Kelvin shuttle, I can only assume you're once again implying that this is an old prop that is being modified for some reason.
This is how wide the principal, 2250s shuttle interior is:
http://movies.trekcore.com/gallery/albums/xihd/trekxihd1353.jpg
This is half of how wide it is:
http://movies.trekcore.com/gallery/albums/xihd/trekxihd0662.jpg
And this is how wide the Kelvin shuttle interior is:
http://movies.trekcore.com/gallery/albums/xihd/trekxihd0184.jpg
While much of the interior decoration is obviously recycled from set to set or prop to prop or whatever, it's obvious that the medical shuttle interior set is not the same as the principal shuttle prop, but instead is separately purpose-built. OTOH, the medical shuttle interior corresponds nicely to the new prop we see, including the forward window, and does not appear to require wild walls in locations where the new prop couldn't have them. In other words, it's a good candidate for an in-and-out prop rather than a mere interior set.
We don't know if the two sections with sliding doors and outer/inner walls used in the "entering the Robau/medical shuttle" scenes were part of this set/prop or a separate two-part set/prop; in theory, the entire medical shuttle interior could have been rather easily carried into the factory and filmed there (while the massive principal shuttle obviously could not). But we have every reason to believe in a rather complete set of the medical shuttle forward half, and in sliding door set/prop - making it eminently possible that we are in fact discussing a medical shuttle prop.
...Which in its original incarnation then clearly has the sliding doors on both sides. So yes, those were ripped out and replaced.
In the alternate theory where the medical shuttle interior set is not part of an exterior prop (a theory supported by the fact that TPTB never filmed a continuous shot of somebody entering the Robau/medical shuttle), and the exterior prop we now see is not an expansion of the one-piece interior set, the doors were only figuratively ripped out and replaced by different ones. But figurative counts, too, as it shows the intent, and the only evident intent.
Timo Saloniemi