You guys aren't easy, are you 
meh, it happens, but in the end we tend to be our own worst critic as artists ;)
ive been stalking this design for awhile and i have some thoughts: that straight line on the underside aft section of the eng hull totally throws off the "curves" of the design, but not soo much as a DRASTIC curve as the original excel, something subtle, but still noticable at the same time, alternatively, you could slide the top portion of that line back somewhat and do the curve. (if that makes any sence at all)
the back of the "neck" could use the same touch as well. take where the back neck meets the hull, and slide it aftwards slightly and add a subtle graceful curve to it, reason being is you have the curve of a galaxy saucer, meeting a dead straight line wich throws the whole look off, that and its the same for the underside of your impulse housing,same as well with the fore of the neck.
other than that my only other complaint is the pylons, BUT i really cant think of any other course of action to take with them other than giving them the sovvy "wing" style wich would not look good IMHO.
keep it up though, i like how this is turning out!
something along the lines like this:
(mind the crudeness.. i cant use PS with a touchpad to save my life)
