Concerning the illuminated areas in the dorsal, I believe we might be looking at passageways.
At first, I used these vertical lines in the dorsal in my draft to hint possible vertical ladders. But on second thought these wouldn't make a lot of practical sense, i.e. while you have 5 crew members descending those ladders you might have 5 guys waiting below in order to ascent.
Therefore, the ladders would have to be placed to allow the quickest passage equally for those descending and those ascending.
The way I currently envision it you have a ladder going down from the saucer and arrive at the bow of E-Deck 3. From there you take the dorsal "promenade" heading astern and descent where the vertical lights are.
It's really difficult, IMHO, to come up for practical purposes the space in the dorsal could be good for (other than cabins for the female Romulan Commander and others).
There could be gravity less than 1 g for training purposes and stuff like that.
Come to think of it, I'd say that artificial gravity control would be best located in a ship's area where there is zero gravity - because in an emergency situation and loss of artificial gravity these guys woul be immediately up to the task of fixing it, based on their daily zero g routine.