No need for the polycro to protect your tent, just spend 30 seconds moving any sharp rocks away from your tent site. However, it is nice to have if you are going to cowboy camp.
I agree with Marko that I'd rather have a down parka than a vest.
I am sure you have evaluated it for yourself, but the JMT would be tough to hike barefoot. Many miles of golf ball gravel, sharp talus, and trails turned over by horses. At least this year you may not have to walk over much, if any, snow.