If all you're looking for is gear and progression, you can probably get by single boxing. Personally, I just get too much out of multiboxing to give it up, from gauranteed loot distribution, to multiple crafts, to being able to solo the weekly.

If there's nothing you like about boxing any more, don't do it. Simple as that. It not like there is any shame in playing just one character. Personally, I use my boxing experience to enhance what I can pull off with just one. Just do what you want to do.