I don’t think this would be so great for the community as players would just go in to creative mode rather than editing their condo for real.
In this situation someone could make a cool condo without even working for it and be satisfied with that. Then they would just stop playing the game because they never needed to work hard to create that cool condo they made in creative mode.
Also your idea of “saving” the condo you made in creative mode just doesn’t make sense. If you were to create something for free, then buy all the items, you’d just be stuck with an empty condo (house, etc.) and would have to recreate the entire structure.
In regards to your conclusion, I think that there is a plethora of creative condos that are very impressive and a sandbox mode wouldn’t make a difference in that.
I apologize if this sounds mean in any way, I’m just sharing my opinion and hope your having a good day!