Do upthrows provide more height midair? Noticed they're often used for extra height. Or do they not get cancelled on touching a wall?

I think they give a tiny bit more height, if not, then it's probably just a placebo.

they give a little more height than regular cap stalls(with normal throws).

ah ok. Do take slightly longer then but have the same amount of height gain per second?

They actually don't give any more height, it's the exact same as a normal capthrow as far as mario's physics are concerned

Huh, do they reduce cap stalling at all?

it is the exact same as a normal cap throw, the only thing that changes your animation and where cappy goes.