I am working or stabilizing some material and was wondering whether upscaling a video sequence before stabilizing it is beneficial and actually tried it, but it did not seem to be better this way. Therefore I am wondering if anyone could explain to me why this is so? Ther eare more pixels for the stabilizer (warp stabilizer in CS5.5) to work with, so why does it not become more stable. Also it seems more distorted after downscaling to the correct resolution, how so?
You don't really gain anything by doing this. Upscaling merely makes the pixels that already existed bigger. You haven't invented any new ones, so you don't have any additional detail in your shot.
Ther eare more pixels for the stabilizer (warp stabilizer in CS5.5) to work with, so why does it not become more stable.
No, not at all. You are merely extrapolating existing info and in fact introducing more deviations. What's not there is nort there. This is simply a useless workflow and you are wasting time with it.