Using The Vault for shuttle dailies would be a great idea.
But why stop there? From the size of the vault you could do a whole series of missions in there. Make it an exploration zone. Take the shuttle in, fly around doing certain objectives and then have to beam into sections of the station for others.
Make it a whole exploration experience in there.
Yeah, I agree. It was such an immense and new type of zone that it is hard to believe they would just use it for one mission and never return to it.