I have a similar squad -with a heavy bolter instead of the missile launcher- and I can't say that they normally gain their points back. What they do is forcing the opponent to take pinningtests, and annoy him enough to prioritize them instead of say, the devastator squad.

I use them to hit command squads and elite units as much as possible.

 

They should be used more as a harassment unit than something that will cause massive casualties.
If I run a sniper squad it will be 8 Snipers and a Heavy Bolter.
Try to keep these guys in cover at all times and avoid moving if possible. These guys are more expensive than bolter marines and not as tough, so you need to be careful not to give your opponent free points.
Don't expect too many casualties against MEQs as they will make there saves most of the time.
If I get 2 MEQ casualties a turn, I'm quite happy and I did have one friend that could NEVER make a pinning test, but again, usually they will pass Ld based tests as well.
The missile launcher is probably out of place unless your go monster hunting with the squad. The Heavy bolter helps to increase the volume of shots coming from the squad.

 

I use them as you have... They make their points back. I put them near the end of the table with some cover (if any) and start pounding especially HQ selections, Elites, more rarely troops!

 

I think the biggest mistake I made was going after high toughness troops, like warthlords, forgetting that sniper rifles have a terrible AP (DOH!) Does GW make a scout model with a heavy bolter or am I looking at some conversion work?

 

Yes they do. I've had a couple ordered from my local shop, they are in the catalog. And they aren't terribly expensive.

 

They are best used against models with super high toughness and a 4+ save or worse. Things like C'Tan, The Eldar Avatar, and Greater Demons.

Edit: We just had a discussion on this a few days ago. Here is the link:

http://www.librarium-online.com/forums/space-marines/113657-sniper-rifle-confusion.html