ZeroHour666, how large do you think "Another Dimension" is ? I better not hear something like "only planet-sized" because even at the speeds Kirby & co. were going (speeds that allow Kirby characters to fly across star sysems in seconds), they kept flying through the dimension for long periods of time without ever reaching it's "end".
Here are a few things the "dimension" contains that you can notice in
this clip : Faraway constellations (white dots almost everywhere in the background), closer stars (the big red ones), and nebulas (those random colorful "clouds" you can see.
Nebulas can be 100s of light years large).
"Another Dimension has an unknown size" isn't gonna fly anymore.
Trivia :
Magolor's home planet exists in this "dimension".