I've been eligible to apply for 13 years, but kept procrastinating, until I finally decided to apply this past August. Although I paid the $675, I completely understand why some people waited until the fee increase was announced to apply. $400 is a very significant sum of money. I'm sure that many filers decided to wait until they had enough money put to the side in order to file their N-400. However, when the fee hikes were announced, these people decided to bit the bullet and come up with the $420, instead of waiting and having to pay more.
By the way, I am completely positive that this is not the last fee hike. When I first became eligible to apply for naturalization, the fee was $95 (and that included biometrics). Over the course of the past few years, the fee was hiked several times. Give it another couple of years, and it'll hit $1,000.