My take is they are worth it at veteren level or above.
Stuck out on a flank where he can observe a possible enemy axis of advance they are sometimes incredibly useful. I've had 1 guy take out 2 FO teams in 1 round before they'd fired a single shot. You can't beat that for points value. Even if they are not that useful, used carefully they can slow an attack down nicely by picking off HQ and other high-value units.
Never use them at close ranges, anything under 2-300m will get him spotted instantly. Left alone, he won't take these shots.
CMBO funny moment #37, my sniper runs into an enemy sniper in a forest. Both halt and try to hide, neither taking a shot at each other as they are too close. It's like they both sat down for a cup of tea on the sideline while the battle raged in the middle of the map.