The question is, do these have any value outside of RP and letting people know you have these designed in your house? For example, would someone be able to come in, head to my small basement restaurant and pay a few gil to eat the food there? Or use my vendors to buy stuff like an emporium?

If not, the only real reason for them would be RP and letting people who like to visit houses what you've got going on. At least there's a message book option. Makes visiting houses to sign their book much better. No more guessing games.