Spark plugs are a supporting mod just like downpipes, filters, exhaust and so on....Are they essential, no.
Yes some people and companies would have you believe they are essential...Colder plugs help extract heat from the combustion chamber which may help in reduce preignition....Higher octane fuel is the best means to help with that condition.
I ran the dog crap out of my SHO and had 22k on the stock plugs with countless 20 psi runs on 93 octane fuel....