I'm no expert, but....Evidence has shown the rear AR bars on some cars can result in lifting the rear wheel. It takes a tight corner, big Gs, sticky tires, big HP, bad driver or a combo. How 'bout this for an answer: "It's all in the combo!"
For street+track, the rear bar is great for keeping soft springs and having the body roll greatly reduced. Take a look at lots of 914 project cars and you'll see the rear bar in place.
If AA thinks 100lb springs are part of an upgrade package you are gettin duped. 100lbs is stock, and 140s are the upgrade. You'll want new shocks YEARS before springs go bad, if they ever do (?).