Overall, for me, it looks as if they have taken a very different design approach for the new Enterprise battle section and warp nacelles/pylons and simply 'bolted' on a slightly modified saucer section from TMP.
Err, a bit of terminology clarification: The term "battle section" is anachronistic in this context. It only has meaning when applied to a Galaxy-class starship, whose aft section is intended to separate from the saucer and function as an independent battleship in combat situations. The proper term for the aft/lower section of a Constitution-class ship is "secondary hull" or "engineering hull." The saucer is technically known as the "primary hull."