@Lonewolf
This takes us back to how to define a requirement:
Nice to have?
Have to have?
It's nice to have and I suggest that yes, you have to have.
If your instruments go haywire then at least you have another very valuable point of reference.
As stated previously, pilots are reliant on their flight instruments. If your instrument readings are questionable than a visual back-up on engines and control surfaces (via CCTV) surely cannot be a bad thing.
The Kegworth accident is an excellent example. If the pilots had been able to visually verify which was the problem engine, the accident could have been avoided.