It sounds like you were comparing apples to oranges.
The time to populate a directory listing is dependent on the number of files in the directory and on the size of the restore_points file. Both WIIMC and WIIMC+ will compare each file name in the directory to those in the restore_points file. So given the same directory and the same 50 entry restore_point file(the WIIMC max) the load time should be the same.
WIIMC+ however gives you options to use more than 50 entries if you wish (in blocks of 50) to a maximum of 500. This allows you to limit the performance impact as documented. It also allows you to compare on just the filename rather than the full path so that files may be moved without impacting the restore_points data, but both of these features will increase the load time if you use them, so make sure they are turned off.