Just going from the optical drive to the hard drive, there is no need for two separate hdds. If you are reencoding the video to another format, then you will see a benefit in speed by using two different drives, one for input and the other for output.
Long term wear? I don’t believe it is a huge problem, though like anything else, the more you use a tool, the faster it wears down.
I don’t seem to wear out hard drives any faster than anyone else, and I do a lot of large file transfers and deletions.