The Paper Mario stages has been analysed in detail by me and it has small details:
The background of the SS flavion part is the same as any sunset background (the following image is from the disc of TTYD):
Notice how the grey thingy are the exact same on the background of the stage. The sun is also the exact smae, so it should be animated with the horizontal lines coming from top to bottom indefinitely.
The blooper is almost exactly like the original model of it in TTYD (was proven with a model viewer for that game using the model files).
The ship is not the same from TTYD and that even ignores the 3 platform. The front wall was removed (probably to not obstruct the view) while the back wall is almost completely removed. You can see that they kept 2 section that are on each side. The stairs got replaced by a slope and it has 2 windows instead of one. The rest is the exact same even the flag on the top. It shows how much work was put to modify the design a lot, but still feel like source material.
Sticker star is mostly the colors being very bright that really is the design of the series being kept. Everything feels flat like the series.
Bowser castle is mostly the same comment I had to say, but I wonder what else is there.
So, very good details on that stage so far.