As we all know that we love our own house, but when we find out another people owning other type of house, we always ponder, why that place have *bla bla bla*?
So, I want to give a suggestion about House Upgrading System, basically it involves currants, ingredients (preferably, planks, blocks, metals, etc) to improve the facilities of houses. There can be a skill designated for this, though, example : Carpentry, Woodworks, Metalworks, etc...
Example If you bought 50k houses, There will be a feature added, such as (the most wanted thing) Herb Planting Box, that can be made via planks, or metals. And maybe another wardrobe, and even more beautiful wallpaper, decoration, etc.
And to 9-10k Groddle houses, maybe give an option to build Animal Pen. and herb planting box too :D
to cavehouses, you can make a better lighting (an old fashioned lightbulb?), a neater cabinet, or even a bed.
The menu to upgrade you house is accessible via Realty tab (After you buy your house). There'll be a button to upgrade house, and then It'll bring you to the list of which you can upgrade
Sorry for my bad english