I can't see where this discussion heading, but the main reason people use sandbox is because it has much more objects, budget and space. The reason people use foundry is because it looks nicer and has a larger variety of movable objects.
Preference Foundry is a great map and so is sandbox but I agree that foundry maps are becoming rare. I am currently making a Resident Evil series including; Resident Evil Mansion from Resident Evil 1 Although I could probably make a scale map on sandbox following the Blueprints of the mansion, It won't have the same feel because it will essentially be a house made out of rocks. So i'm making it on Foundry so it Has more of a feel and it's a challenge to make Because of the space and less materials. i'm not saying either map is better or that you should not use sandbox for buildings, just my preference on my own creation.
Forge World is Nearly Within Reach... It was great for its time. Of course they are; Sandbox is superior for most maps. Please don't; Reach is less than two months away, and your idea isn't original. Wait for Reach and maybe you can be the first to make a scale reproduction wholesale. You enjoy having a harder time creating maps? Perhaps you should stick with Forge, then, and forget the ease of Forge World...