God, Trumpet, Nerf, Pipe Band, my dog, Sci-Fi/Fantasy, orchestrating/film scoring, Stock Class Paintball, Canoeing, celtic music/metal, and general shenanigans associated with working full time and married life.
There's a lot to be said for aiming down a barrel. Since most nerfers don't have to worry about shot placement very much (ie. aiming for "kill shots", vitals, etc.) looking down the barrel does a good job of "close enough" for nerf. Hit the body, it counts. No need for minute adjustments, etc. It was said earlier by someone in this thread to "make your gun your baby." Very true. A gun with well-adjusted sights you've never shot before won't fire as comfortably or accurately as one you've spent several afternoons shooting in the last week. Vacc's got an excellent point here. The more time you spend working on building sights to make your gun more accurate, the worse off you’ll probably be mid-round since you’re fiddling with your contraption. Sights don’t make guns accurate. Guns are inherently accurate, or they’re not. Sights just help YOU, the user, fire the gun accurateLY.
That being said, there is a time and a place.
Crossbows, for starters. Crossbows have a hunk of shell in the way, preventing one, generally, from looking down the barrel (this is assuming that you shoulder the xbow when firing it.) My barrel, for example, isn't long enough for me to look down the barrel. Instead, there's a crack that runs all the way down the gun that separates the two halves. Doesn't matter what gun you own, if it was made by nerf, I can almost guarantee that there's a crack running down the center. If you set up your barrel to be in line with that crack from left to right, you can use it. In the case of the crossbow, you can set up your barrel to be vertically in line with the flat space on top of your shell, and that space can help you quickly level the barrel. Not so much an annoying accessory that distracts so much as something to get used to. It happens quickly, and doesn't get in the way. Just practice.
Then there are annoying blasters that have curved shells. Like, oh, I don't know...the whole airtech series. If you're trying to pull off a good placed shot with a 2k, you'll probably look down the center crack to line it up. But then there's that shell. It's curved, so there's no simple or practical way to know if your barrel is actually pointing at your target, or if it's aimed up (or down) enough to miss. In a situation like this, an actual sight can be implemented. It's by no means something to be used all of the time, as sights CAN easily distract as much as they help. But a simple tube or other form of "peep" sight that allows you to center your target in it, with zero magnification and use the circle of the near and far ends of the tube to align the shot, can be invaluable. The trick is to attach the "peep sight" to the top of the gun in such a way that it is horiontally aligned with your barrel. If your AT2k's barrel is pointing way up, point your tube up evenly. Aiming during those few occasions of a round when you have a quiet moment to take aim from a bit more of a distance then becomes a matter of lining up the two ends of your tube as though they were concentric circles, perhaps adjusting slightly for distance, etc. The less complicated the sight is, the better. No range markings, no fancy adjustment capabilities. Just lined up.