MotionX GPS doesnt support auto routing MotionX GPS Drive does. You can hit go to a destination in MotionX GPS but it will just straight line you there.
As for importing tracks I just use the email method, just email the track to firstname.lastname@example.org
and open the reply you get back on your iphone and follow the instructions. I find it easier to make tracks in google maps vs google earth mainly because my laptop is almost 10 years old and slow.
To make a GPX in Google maps:
1 go to google maps
2 hit get directions
3 enter starting and end point(s)
4 drag to change route until you get the route you want
5 scroll to the bottom of the directions and click "save to my maps"
6 go to my saved places and save the KML file
7 go here: http://www.gpsvisualizer.com/convert_input
8 convert the KML to a GPX file
9 email the GPX file to email@example.com
10 open the email you get back and follow the directions
11 in MotionX hit menu then tracks and you should see the track you just added and be able to follow it
Once you do this a few times it's a pretty easy process, if you use Google Earth I'm pretty sure you can skip the step of having to convert it because you can save tracks as GPX files using Google Earth.