A friend made good use of a lone Shooter under an earlier version of DBM, with a West Sudanese army (all right, it was Artillery (X) back then).
Funnily enough, before the comp in question, he'd gone around the club and asked people whether they'd spend the points on a Shooter or more Bow. I, along with everyone else, said to leave out the Shooter and take the extra Bow. He ignored us all and took the Shooter.
And weren't we silly. There were a couple of times when opponents simply couldn't avoid getting in front of the Shooter, and they paid for it, especially when they were assisted by nearby Bow. Much more effective than a couple more Bows.
So the key may be not to make too much of an effort to *use* them, but simply to integrate them into your army, and take advantage when your opponent's troops get in the way. Also, consider how many PIPs your opponents may use trying to avoid the Shooters, such that they waste PIPs which could be used elsewhere, even if the Shooters don't get many shots in. This suggests they shouldn't be massed, but split up among massed Bow.
The overall effect therefore shouldn't necessarily be judged solely on how many casualties they cause, but how their presence plays on the minds of your opponents - they get so obsessed dealing with one threat that they forget about all the others.