Adding weight will help to build larger and stronger muscles without a doubt, however, it will also put extra stress on your lower back so a proper warm up of the lower back is necessary before weighted hanging leg raise exercise. I always perform two sets of hyperextensions before I start doing my weighted hanging leg raises.

You can run your sets in a manner where one rep is with knees bent and the following is where feet are straight out in front of you and see how this works for you. Will be very hard to do this with weight though.