Orvis, you're using them exactly how they're supposed to be used.
Velites are skirmishers, whose primary role is to screen the main force while harassing the enemy.
At first, I'd doubted the effective use of any skirmishing light infantry.
Kinda impossible to screen your infantry assault force from an enemy that can pan the camera view directly over your head.
But they're excellent for diversions, provoking your enemy into an ill-timed charge and my favorite strat so far - engage them with a phalanx marching straight at you. They won't do that much damage but they will keep the phalanx's focus while you move your equites (and if you're lucky, a unit of principes or hastari) behind them.
Works like a charm.