The answer is simple: no. No, one guitar is not enough. Here's why.
Different Guitars = Different Vibe
Perhaps you really do want every one of your songs, and every part within a song, to sound exactly alike. Hey, we understand that you want consistency, and that's okay. But the reality is that it's likely your music deserves better than that. You might have a song that is edgy and bright, and another one that's deep and dark. A big step in achieving the different moods of a song is through a variety of tones and styles you can much more easily get on different guitars than you can using just one. Also, there's a technical reason for using different guitars on a single song: phase. A multitude of tracks using the same instrument will often cause phase cancellation. All of a sudden, those great tones that sounded so good on their own start to become weak and small because the sound of that one guitar is being cancelled out by the layers of the same guitar on the same track.
Many players use more than one tuning these days. Some dial the whole guitar down a full step (D tuning), or two steps (C tuning), or more. Much more. Others use alternate tunings like DADGAD, or Drop D, and so on. It obvious that standing there onstage while you retune your guitars isn't the makings of a good show. In the studio, having to constantly tune and retune your guitars isn't the best creative situation, and also leads to premature string death from the constant changing of string tension (and it's not all that great for the guitar either). Having a few guitars around means you can keep one for a particular tuning you use often, and have the other to instantly go back to your standard tuning as needed.
Maybe you have one guitar, and that's your style, your vibe, whatever you want to call it. The look of you standing onstage with that one guitar is what you want on posters and magazines around the world. But the reality is that different songs (or different bands you might be in) each call for their own feel. Note that most of your favorite guitarists likely turn to a variety of different axes for different songs they do. There's a reason for that; they choose the best tool for each job they take on.
Since nearly all of us at ESP are musicians, we know what it feels like to get inspired by picking up a diferent instrument now and then. Sometimes when you're stuck in a creative rut, turning to the same chord types and scales over and over again, the fastest way to break out into a new playing mode is to pick up a new guitar. Sometimes, the act of trying a different guitar or bass will literally lead you into writing a new song, based on the inspiration of the different feel of the neck, the weight of the body, the tone of the pickups, and more.
What If I Can't Afford Multiple Guitars?
Then you're like most musicians, and we're sure you'll make the best with what you have available to you. But ultimately, if you're serious about your music, at some point you're going to find a way to get that second (or third, fourth, and so on) guitar or bass that will keep your sound fresh and keep you inspired to do more and more cool stuff.