Another thing to consider is technology is changing so rapidly now it's hard to even consider what may come next. A company here in New York is making wee motors small enough to drive optics for cellphone cameras. I mean, that's tiny. It's not a motor in a traditional sense with a rotating coil and all that, it operates on a different principle.
When I started manufacturing stuff in 1989 I remember it being possible to get a tolerance of .010 repeatable over many cycles. As the machines improved from 1989 to 1999 and further out to 2008/9 I can hold .005 now without much effort on a 140 ton bending press. The new ones that they have coming down the pipe will be able to hold .002 over a thousand cycles without flinching.
Who knows? We could be looking at some kind of adaptive construction materials and technology that changes the shape and thus the location of the structures on the fly, in fact you would need something like that because the now exposed skin of the saucer and the now exposed skin of the neck will heat and cool and expand and contract different amounts as both ships are in different enviroments after separation... The saucer could be called upon to exit a solar-system at high-speed while the stardrive is duking it out in the atmosphere of a Class-M planet with a Leggs panty-hose container attached to a shampoo bottle.
What I'm getting at is we honestly don't know what the Enterprise-D is really capable of because we cannot conceive of the incredible technologies required to build her.