I would recomend changing shoes at Robinson Flat for two reasons. First, there is a better than average chance that there will be water before climbing up to Robinson. Also, there will be water in sections after cresting Immigrant Pass. The second reason is that, up to Robinson Flat, most of the course is rather rough trail. After Robinson, the course is mostly dirt roads or trail with relatively good footing. If you are one who wears trail shoes, I would recommend them up to Robinson and then change to good, cushiony road shoes. The only other place where a shoe change will be necessary, is at the river crossing, provided they don't ferry you across this year.
Have a good race. I wish I could be there this year but, sometimes you gotta do other things.