I've not noticed that, although that may just be due to the fact that I generally MAPIMPORT Shapefiles, and only use MAPWSPACE for drawing queries of the imported Object Data.
What exactly are you 'bringing in' from the Shapefile(s) using MAPWSPACE?
The only thing I have noticed slowing a session to a crawl, is a pick of even a single imported Polyline that has too many vertices, with no real way to force a deselect (until the select is finished). GRIPOBJLIMIT only accounts for the number of entities selected, and not the max number of Grips to be displayed.
Cheers