Call around and get some quotes. We had one guy quote $10k without a new board. He sounded like he didn't really need the work. Was complaining about what a dirty job it was, and how hot it is in the roof. Called another guy and he quoted $3500 including a new board. He brought a bunch of guys and was done in a day. Made it look easy, and they tidied up before leaving.
We had a lot of old fabric-wrapped wires, perhaps original from the late 1920s. I had a lot of peace of mind once the job was done. I definitely felt it was money well spent.