While these are some known limitations as you reach the extents of our zoom, there are some tips to help improve what you are seeing.
First, in SpaceClaim Options > Popular there is a Rendering quality setting. This determines the level of tesselation of your model. Bumping this value up from the default of 3 will result in smoother looking curves and edges when zooming in. Depending on your graphics hardware, there will be a trade-off in performance, so you may want to play around with the setting to find the optimal value for you.
Some of the streaking or patterning you describe could be cause in part by faces being coincident. If two faces are right on top of each other, sometimes they both appear partly rendered.
I am not sure what you mean by parallel objects becoming non-parallel. Could you elaborate?
Also, there is a workaround of sorts for all of this. You could scale your model up while working on these fine details, and then scale it back down by the same scale factor once you are finished.