Do I even need knock sensors?
 

I'm about to have the starter replaced on my 2004 Boxster, and some people recommend having the knock sensors replaced at the same time, if you are accessing that top-of-engine area.

I religiously use nothing but Sunoco Tier One 93-octane fuel. Do I even need knock sensors?

Yes.

you could choose to not replace them however to run without them would result in a disaster

Yes you need them. No, they are not a common failure item....

Yes. I think they tell the ECM about the octane of the gas you're using. ECMs don't like not knowing.

Not to mention, I suspect that the omission of the knock sensors will trigger an error code in the engine management system, and all that this entails.