@juggle: The first thing that becomes apparent to me is your use of dash dancing and double jumping. You do these two things a lot and in very readable/non-threatening ways. I'll get back to you more in depth but at the moment I am leaving for work :D
p.s. your gentleman is tight as hell tho. You also seem to have a really good grasp of the bair. I feel like you don't throw knees out nearly enough, although I don't mean. .(
http://www.youtube.com/watch?v=rOpRDbvq6OQ&t=1m3s ) . . launch yourself desperately at the opposing character with knee, just kinda space it so that they can easily run/jump into it without being able to grab you for it. You can kinda use down air in a similar way.
What i mean is
http://www.youtube.com/watch?v=rOpRDbvq6OQ&t=1m06s After the falcon kick here you're soft dash dancing (slow, very far away). . . you jump in and . . . double jump. there's no stage control here. Vanz is able to pull and regain half the stage. Part of this is intuition and part of this is experience. I'm not really firm inside the peach/falcon match up (fish for grab, combo, iirc??), but that's kinda beside the point.
http://www.youtube.com/watch?v=rOpRDbvq6OQ&t=2m41s So here you come back, kinda . .. malfuction on the way down and its right back to dash left. . .. dash right. . . .dash left. . .. random read attempt. . .
sad end to the first match.
http://www.youtube.com/watch?v=rOpRDbvq6OQ&t=5m10s
The things you do well, you do extremely well. vs. sheik I probably can't help you at all :D
Vanz is just raining moves on you so there's probably a lot more pressure. This second match was pretty ugly :/
http://www.youtube.com/watch?v=rOpRDbvq6OQ&t=5m59s - 6:04 (derp dancing)
My conclusion: you don't have a lot of experience vs. sheik and so, you weren't really able to play vs. vanz as a player.