Is it worth turning a used Honda Civic (100,000 miles) into a tuner car?

I recently bought a used 2008 Honda Civic coupe with 100000 miles on it. It runs excellent so far but I would like to upgrade the motor and add accessories to the body. My main concern is the motor, as I don't know much about mechanics but I do know I don't want to ruin a good thing if it runs as well as it does, at the same time and for a secondary reason for rebuilding I would do it to extend the life of the motor.
Are these good reasons?
Should I upgrade even if it runs well? Or will I ruin a perfectly good motor?

Thanks to all who read and advise this novice!

Read more: Is it worth turning a used Honda Civic (100,000 miles) into a tuner car?