My theory is this: You needed bumpy hull plating like on the NX-style ships way back when but when shield tech became better and more distinct form mere "hull polarization" then Starfleet ships became basically smooth-hulled, hence the smooth white / light grey of the cruisers like the original Constitution. Hence, i think in the early era you can very well have "bumpy-hull" ships alongside "smooth-hull" ships, as long as the bumpy ones are not many and are on the way to being phased out or uprated.
There exists a precedent for this in TNG: In the second season of TNG they built that 4-foot long model of the Enterprise-D, much smaller than the 10-foot one, but the smaller one was better detailed and had bumpy plating all around, like the ERTL/AMT model kit that was released. Hence, we're supposed to assume that the Galaxy was always like that, with bumpy plates. HOWEVER, if you examine the Sovereign you'll notice that although there is patterning on the hull, there is no bumpiness, it is all smoooth. So, you can have these two kinds of hull plating in Starfleet without any continuity problems, in fact you can see it as two avenues of design for Starfleet engineers.
Topic: My first model in well over a year! Pics inside (Read 11884 times)