Insulation is one of those things that you do not get any visual appreciation out of or even any return on the investment, but it can change the comfort level of the home drastically if the existing insulation is in bad enough shape and if it is installed properly.
It is also a project that lends itself to doing it yourself, though like all projects that has its drawbacks also. For example, as a byproduct of not being able to see the insulation, it is necessarily in out-of-the-way places that can be very challenging to get to. For example, if you want to install it in the crawl space, you need to get the rolls under the house and crawl around in a cramped space trying to cut it and get it held up so you can staple it in while trying to keep it from falling back on you. You will often hold the other end of it up with one foot while trying to get the paper unfolded to staple to the joists.
Of course you need to know the joist width so you can buy the proper width of insulation. This is usually 18 inches or two feet. Insulation can be nasty to work with because fibers are constantly falling from it onto your face and eyes. It is crucial that you wear a breathing mask and glasses while working with it.
You should do some learning about this type of project also before getting started in it. The more you learn the better. Once you have acquired the skills and know-how, you will better be able to determine whether to hire it out or do it yourself.