Hi Rabz,
Just as detailed as it needs to be to capture the ideas you are trying
to represent ...
Another way to put it is ... where the models in EXP2 were simple
massing models, the models in EXP3 should be Architecture with
interiors and believable spaces.
Keep in mind the poly limit of 10,000 polygons though. I just left
some advice on the sandbox2 tips and tricks page about this.
Cheers