I think the notion of most of Gideon being given over to agricultural space (thus crowding the rest of the populace into futuristic domed cities) is a great one and solves one of the chief nits
of the episode - the issue of feeding the sea of people.
It also explains how the Gideons managed to find the space to build
their starship replica, which if their entire planet is shoulder to shoulder ought to be have been impossible - however, giving up a little of their farmspace for such a vital project is well within the realms of possibility.
How they got hold of the exact plans of the Enterprise in the first place? Erm......