Personally I don't try to figure the canonical extent of the characters' abilities..
- Yukari, for example, mentions that she can't transport many people to the Lunar Capital
- Cirno, who has a not-so-vague ability, can be exploited to have ability over atomic movement (the "entropy" thing)
- Suika could become many times larger than the universe (and since she can manipulate not only her volume, but her mass as well, she could still be more dense than a.. neutron star, for example), her powers have no known canonical limitations so far
- message of the day: the vagueness of canonical descriptions and limitations give ground for speculations like these above, and gives us the element of doubt, since none of these can be so far disproved, or confirmed. Also, providing a canonical answer cuts out such questions, serving as a limiter for people's imagination (though there are some answers that lead to more questions or give more material for people to explore and question), so, canonizing an answer is something that must be done carefully.