Distinguishing "Liberal" & "Social democratic" seems very sensible to me, assuming the survey should have good discriminating power among as much of LW as possible. On the last survey the two most popular categories were "Liberal" (35%) and "Socialist" (32%); it's not as if either category is superfluous.

On similar grounds, I think there's a case for rolling the "Communist" category into the "Socialist"/"Social democratic" category to make a broader "Social democratic, socialist and Communist" category that still splits the more leftist respondents from the more centrist. One could then replace the old "Communist" category with a new "Reactionary" category, improving the survey's discriminating power while keeping the total number of categories constant.