1st point, since XvT is getting on in years (C 1997), the tone is very easily reproducible, and doesn't seem to have any sort of ill effects from any compression, I've posted the wave file here -
http://www.wedgenet.us/TGT-LP-2.WAV - Opera users make sure to right-click and save as. If this is outside of legal rights, feel free to edit out this line.
From this point forward, here's a disclaimer: though I'm trying, I'm afraid I'm not up to speed on where everything hides in FS2SCP or how everything works, so it's quite possible I'll make a completely inane suggestion.
For making it optional, would it be possible to implement the following?:
1. Include three new variables in the player file, for instance, bool looping_lock, string ll_string, and bool ll_override. The first is pretty self-explanatory. The second would be a filename inside of a data/sounds folder, which would allow the player to specify any sound he or she would like to use
and allows the feature to be used on any ship/weapon which did not have this defined. The third would allow a weapon or ship entry (depending on the implementation) to override the player-defined sound - which leads to part 2.
2. Create a new variable in either a ship or weapon definition called $looping_tone. Whether this would call to sounds.tbl or straight to the file is not my decision (and, if my assumptions about the format are correct, it'd be to sounds.tbl). This would allow mod-makers or whomever pleases to customize the interface even more, but since it works in conjunction with ll_override, the player could revert to his/her sound if he/she found the mod-maker's sound to be less than optimal.
As for the WC thing, I'm sure they'd appreciate that

I rather prefer the moving reticle now, as it kind of clues me in as to what I need to try to do to gain lock - or at least I think it does!
For the different reticles and such, speaking from the point of view of someone that can get through helloworld.cpp and not much else, wouldn't it be theoretically possible to define the texture/icon to use and the scale with which to use it from inside the weapon definition in weapons.tbl? At that point I would think it'd be a relatively minor task of simply switching transparencies appropriately.