For me, better suspension allowed me to go faster in serious twisty stuff, more comfortably, and safer.
IT doesn't turn you into an instant racer, but allows you to get more out of your bike, and you.
For a 150 pound rider, sticking to flat roads, and happy with it, the stock suspension is OK. For touring, or anyone wanting to ride somewhat AGGRESSIVELY on a twisty road, it sucks......