The underside details, even if painted, still look stunning. They didn't even look that way, and I would probably have never even noticed if you hadn't posted close-ups or mentioned it.
: What you say about the Sovereign class having unrefined aspects and errors in her design is true, especially the placement of the impulse drives (I would have probably put at least a pair in the nacelle pylons; those, she would use while together, while the saucer impulse drives would work brilliantly only after the saucer section had cleared the engineering hull) but she is still a beautiful design. There is a difference between looking like trash, and being unrefined or under-detailed.
The Grandeur has surely benefited from having a much longer time of development, and I get the feeling that the deadline prevented John Eaves from making further design refinements to the Ent-E, and I speculate this is why she lacked visible aft weapons on her engineering hull, like the ones she had in Nemesis.