I would think that a "boxed-shaped" vessel might pose some problems in terms of speed. Sure there's no wind in space, but look at a transport truck versus a car on the road. A tractor trailer isn't as aerodynamic as a car, and to counter for that they even put that slope attachment on the top of the cab to try to counter the wind against the truck. I would think Starfleet would need something that was more aerodynamic than just a big box.
But for something to house a Vesta you'd need something like that giant Enterprise from the DS9 Millenium trilogy.