-I'd want to de-clutter the design, in other words, remove all unnecessary junk. The photon-torpedo box has a bunch of gadgety things on them for example, the warp-nacelles on the front have small box shaped thingies, the warp-engine's amplification crystal, and the lighting boxes (which extend out from the nav-dome)
are unnecessary (The early TMP design didn't have them until Doug Trumbull got his hands on it)
-I'd want to make sure all the docks are correctly to scale (7-feet); and to remove the dock on the side of the torpedo-tubes
-I'd want to remove the grilles on the front of the nacelle and instead use a smooth nacelle cap like some Phase II designs (no grilles)
, with a flat gray color that's a little darker than the rest of the hull so it stands out.
-I'd want to round out the gangway hatch on the edges and add another hatch to the starboard side.
-I'd want to drastically reduce surface detail to make the ship look more clean-cut like the TOS design. The pearlescent coat I actually do like but the detail is otherwise too much.
-I'd want to move the windows slightly higher on the saucer-rim as they are a little too low for observation ports.
-I'd want to reduce the size of the windows of the O-lounge as they're more than 1.5 decks high.
-The area which houses the airlock and hatch behind the bridge, I'd prefer to slightly (mostly the vertical lines)
round it's edges a bit... it appears just too boxy and unrefined.
-I'd want to either make the impulse-deflection crystal glow pattern more like the Enterprise-E's deflector (in otherwords most of the surface doesn't glow, with a small amount of glowing area rather than the impulse crystal which is the opposite)
or just keep the impulse-crystal a gray or white color with no glow -- it looks good that way (I saw some early pictures of the model -- not bad)
-I would want to rid of all the crazy gridding on the saucer rim. Too much deflector gridding, not needed! The radial grid lines could simply go from top to bottom along the rim and that would be good enough.
-I at least would consider replacing the recessed grilles on the TMP design and replace them with the raised grilles like on the TOS design (The skin is kind of thin and those grooves could cut into hull-space)
although the grid lines on the secondary and primary hull I'd keep the same (except on the saucer rim)
-Remove unnecessary windows on the engineering hull (particularly the back area)
-Remove the botanical garden windows -- cool as they look I don't know why you'd need them (It's technically possible to produce light at the wavelengths produced by the sun and at appropriate energy levels and to supply the plants with CO2/O2, and water)
unless it was a rec-room like facility -- but that's supposed to be up on the saucer...
Basically, I'd want to de-clutter the design, simplify it, improve the accuracy of the sizes of the hatches and stuff and make sure all the windows are in the right place, and make sense.