On the weight it should help overall traction and with the spool if one wheel is spinning the other is also and then the car wants to step out. The torsen/true trac will try and stop the wheel with no traction from spinning and actually send some of the power that was going to that wheel to the one with traction.
I wandered into this thread to see what's going on and I'm interested to see that someone else is also going to some trial and tribulation with a newer car. We too (myself and Skip Pipes) have been spending more time trying to get the car situated than making high speed passes. The roadster has all the right things going for it... well constructed, highly adjustable suspension, long wheelbase (for a roadster), good weight and weight placement and yet the car didn't really like to go straight.
I quoted the above because we started with a torsen and have since taken it out. It just simply did not work correctly and we don't really know why. What's strange is that it's worked well for others but was disastrous for us. Since day one, the car would quickly pull to the right at the top of any one gear where the engine is really starting to make a lot of power. We made a short list of possible things that could attribute to the problem and the torsen was the last item as it really wasn't believable that it'd be the problem. We replaced all the Speedway heims on the car with FK heims as some of the Speedway pieces had developed a click to them. We ditched the tape measure alignment job and took the car to an alignment shop. We put the tires that the car was originally built for on and re-adjusted the suspension (had started out with shorter rear tires which made the car too low and required lifting the suspension to get the right ride height). We added a steering stabilizer/damper. We dialed in more caster. We did all the right things that should have made the car happy but the torsen was still acting up. On a test run, everything was going great and the car was going straighter than it ever had and then bam, the torsen wigged out and bad things happened. Basically, what we think was happening was that the torsen was torque biasing for no real reason and sending all the power to left wheel and the car would "rear steer" off to the right.
Well we finally saw the light and took the torsen out. Tested again and viola, no pull to the right at the top of second gear. I used to not be able to rev past 7k in second gear and now I can go 8k+ without the car turning. The only problem now is that the car drives like an open diff car which is to say that the car basically wanders down the course. We ran at El Mirage last weekend and had mixed results. I only managed two 160 passes when the plan was 160, 180 then 200. On the last pass the inertia switch popped. I find that I'm doing more conservative recovery driving and less aggressive WOT fast driving. I've always driven an open diff roadster at El Mirage and I know that rarely does an open diff roadster ride like it's "on rails" or go perfectly straight - it just ain't so. The biggest diff (no pun intended) between Skips roadster and the Stewart Family roadster is the new roadster makes about 5 times more horsepower than our old one so the days of holding it wide open and pointing down course are long gone.
Anyways, long story long, I totally understand and feel you on the getting uncomfortable real fast when a car gets twitchy. It's always better to back out of it and ease back in versus staying in it and trying to "drive through it" because that's when bad things happen. Rule #1 is listen to your gut. If your gut says lift, then lift. As for us, we've got a few other small things to try including adding in a little weight. We're at 3000 lbs wet with a 45/55 front/rear distribution and nearly even from left to right. The other thing working against us was the course wasn't very good - not terrible and not great, just not very good. When the car went from far left of course to the middle and then from the middle to the far right, I kind of just lightly suggested that we think about going to the left some with the steering wheeo. It shouldn't ever be a white knuckle, fist over fist kind of deal - just gently guide the car using small steering inputs with your finger tips. Anything more than that and there's probably something wrong.