I was able to import the combined data from both the wil file and the rickenbach file. Until I saw them together, I wasn't sure why you needed to "merge" them. As @NZSnowman pointed out, this is a lot of data points. The final result is about a million entities and a SketchUp file size of 170 MB. The plugin is not fast ... on my computer it took a long long time to complete. Also, note that when it finishes, you will need to zoom extents to see where it was created. The coordinate data is imported as if they were in inches ... the data will be somewhere northeast of X = 2,720,920 & Y = 1,256,200.
For testing purposes, you might try running the plugin with a much smaller range of data. For example, 2721335, 1256535 to 2721920,1257100. Also, if you open the Ruby Console window before running the plugin, it will display any errors that might occur.
You had originally asked about the -9999 values. These are used to indicate datum points in the data that are not valid. When imported, they "hang down" like this:
Opening the group and selecting the "tail" with the right-to-left crossing window:
You can then delete the "tail" and zoom extents on the result. Here are plan views of both files with the data imported and exploded over each other:
If you are wanting to learn a little Ruby to assist you in doing this yourself, I'll be more than happy to help. The RBZ file is a RB text file that has been zipped. The original ZIP extension was simply changed to RBZ. You can change it back to ZIP and unzip the file or download the RB (text) file from the website (RB refers to the RuBy language).