Is it worth it to insulate hot water PEX tubing?
It's definitely worth it if you are running new pipes or the existing pipes are easily accessible, but if you have to lift boards etc. to gain access probably not.

PEX is a very good conductor. One of it's uses is for under floor heating systems, so if you are using it for delivering hot water the it's definitely worth insulating it. This is true of copper pipe as well.