More sounds could be useful, sure. I wouldn't be too happy with replacing 'classics' like 10mm pistol, AK, shotgun etc. But some guns, especially those who weren't much of a use in original Fallout (like XLwhatever, M60, mauser) could have their sounds from Tactics. Well, this + sniper rifle, which don't sound as a sniper rifle at all.
And here would be an additional demand that you need original files from Fallout: Tactics.
That's the problem. I don't know if cutting out people who doesn't have FT is a good idea. It also couldn't work like the music issue, 'cos making some guns silent (because you don't have the files in the sound folder) would be a serious drawback to some players (especially during bigger PvP battles like TC)
I can see this as a good suggestion, if it would be made like that: All guns have classic sounds, but some of them can have new sounds if you'll copy certain files from FT. So a sniper rifle sounds like a hunting rifle unless you put a certain file in the sounds direcory - then it sounds like a sniper rifle from FT.