- (out-of-universe) Use the same set for both bridges, just different lighting.
Would that be the standard "danger" lighting used so much throughout Voyager? Makes for some very dingy scenes!
- Make the bridge itself transportable. Bridge units are already made to be swapped out and replaced easily, after all.
Funnily enough I was going to mention this, but it made my post overly long! It's just the system I used to use with the Lego Enterprise I made as a child. In practical terms it feels very "Thunderbirdsy" but hey, what's wrong with that?
Or (in universe) have the main bridge located in the secondary hull to start with, and then have a alternate bridge located in the saucer.
Massive moving bridge-elevator shafts aside, the "main bridge" would pretty much have to be in the Secondary Hull. But then again, why not? The Secondary Hull is the "business" section of the ship, the Saucer is where the families, living quarters and recreational facilities exist. In essence, it's a mobile starbase.
As for the equivalent control centre in the saucer, it would really only be needed to pilot and navigate the craft, perhaps just a few consoles adjacent to one other (think an updated version of
TOS's Auxillary Control).
Oh, and don't have the main bridge on top of the corba neck, too exposed by far.
No argument here. The TOS Enterprise's design meant that most parts of the ship were more or less equally exposed to danger from phaser fire, so why not put the Bridge up there? By TNG, there's really no justification for such absurdity.
Actually, the justification is that the original design of the Enterprise-D model was not done with saucer separation in mind at all, and the Bridge itself (according to the early sketches) was a massive multi-storey facility not unlike the Rec Deck of TMP. A Bridge like this would be
the main Bridge without question, so the saucer (AKA
main section) would be the only fitting location for it.
As it turned out, the E-D Bridge was not a great deal larger than the Battle Bridge (also TMP, of course).