Will using premium fuel prolong the life of a 98 civic?

Yes and no. It will prolong the life of your engine because your feeding it better fuel that burns easier. But it wont prevent other things from failing ie: transmission, axels, fuel pump

i could not discover any components saying that the EX demands top rate. This thread has somebody reporting 37-40 MPG with undeniable unleaded in his Civic EX. hardly any 4-cylinder, "regular vehicle" engines require something larger than popular gas, and you will't get a lot greater regular than a Honda Civic, so if it required a a techniques better grade, you will think of that they had carry that to the motive force's interest. If it does not say on the dashboard or close to the gas cap which you will desire to apply a a techniques better grade, i does not concern approximately it.

No because base model civics should use regular gas... Using the premium gas will make it's left end quicker. Unless you have a civic SI then you use premium. Just use shell or chevron gas for top quality.

20 years ago the answer would have been yes, but today it is no.

In the Olden Days premium fuel usually had more detergent than regular grades of the same brand, on the theory that high compression, high performance engines need it more and customers who wanted better gasoline would pay more. In 1995 the EPA released new rules for detergent levels in gasoline. They said lower levels were okay, so pretty much all the chains dropped their detergent level in all grades to the newer, cheaper, level. The big problem was the EPA was full of EPA stuff. The new levels were nowhere near adequate to keep intakes and combustion chambers clean. In response, BMW, GM, Honda and Toyota got together to form the Top Tier consortium, and in 2004 launched the Top Tier licensing standard. Brands that maintain a Top Tier license are contractually committed to maintaining an effective level of detergents (the level is given as test standards and as concentration) for all grades at all pumps within that brand. The licensed brands are listed in the first source... some of them are inexpensive brands.

In 1994 (well, before your Honda was made) premium fuel would extend the life of your car; today regular fuel from any Top Tier station will do the same.

it wont because the engine is designed for lower octane rating fuel

Nope, will just be a waste of money.

No.