If you do scaling/parenting, the cloth is not supposed to rescale with the parent..  What you need to make sure is that the character is scaled -only- in the first frame. Make sure that all the values are set to 100% in the final pose, or it will just scale the whole thing.  Also make sure to set the keyframes to linear in the animation palette, this will give you better results.

I had a lot of problems when I tried to do morphs from cloths and then apply it onto a figure.. The vertexes are often out of whack too.

There's a method to do this I have considered trying, but haven't done yet (Maybe someone else)

That's to make/use a bodysuit, run the cloth simulation with the bodysuit, so it covers the whole character and shapes as you want (Into a zero pose but with the character's morphs on it) Then you could export the prop and then use something like Morcloth to apply this morph to pretty much any clothing..