A friend of mine had an SVT that was totally modded out...she had a spec stage 3 clutch, fidanza flywheel, and the quaife LSD. We swapped cars for while (like, for a couple weeks) and that made me want her clutch, but the LSD wouldn't be worth it, to me.
The only noticeable difference it made in street driving was that while turning, the car wouldn't "return" to a straight line. If you didn't force the wheel to straighten out, you'd just keep on going in a circle. Even with all of the mods she had done (cam gears, exhaust w/ ORP, UDP, CAI etc...) I still beat her in races only having my few mods and Tom's tune. It pissed her off, to say the least...she ended up selling the SVT.
So yeah, there is definitely more grip and control with the LSD, but NOT worth the cost if you aren't competing in racing events.