Actually I think theres much more to Kuja's actions then that. There are multiple factors leading up to his desire to destroy all.

First off, of course, would be his Narcissistic nature of course, as shown by that quote.

Theres also another crucial reasoning behind his actions. Since the begining, Kuja's fate was planned out for him. Even being replaced by Zidane was part of the fate given to him by Garland.

Essentially every action he had taken was a direct attempt to defy the fate given to him by Garland. However all up until Terra, he had failed.

What came their was the death of Garland and the Awakening of Kuja's trance. It was here that Kuja realized something. No matter how much he struggled, no matter how much he fought, he could never escape the fate given to him by Garland. The destruction of the Crystal was the last attempt to take control of his own fate, which overall had been his goal from the beginning.

So to say Kuja's goal was simply because he didn't want the world to go on without him isn't fully true. It is simply part of his reasoning.

And the final piece of the puzzle, simply look at Kuja's upbringing. He was raised to be Garlands angel of death to cause chaos on destruction on Gaia in order to destroy the Eidiolons. His whole life that is all he has known.

So, what is a Narcissist who has known only destruction to do when he realizes he is locked into a fate he can never overcome, regardless of how much he struggles?

To be honest, I can't think of many things outside of wiping out existence as we know it. It definitely satisfies all aspects of Kuja's personality and dilemma.