Admittedly, I wouldn't mind 3x3 displays as a final goal prize as long as everything is scaled well; they can still be just as detailed as some 4x4 prizes and the smaller size makes it easier to place in the restaurant space. However, I'd much rather have a 4x4 for two reasons: (a) the achievement feeling, as you described, and (b) considering the gem price tag that's being attached to the final goal prizes nowadays, I'd much sooner pay gems for a second 4x4 prize than a 3x3.
That being said, I do hope we return to getting medium-sized interim prizes. It's weird to have two 1x1 prizes and then go straight to a 3x3; it doesn't really give the sense of achievement as you complete the steps
I second the request for a door!