The Speedpark is more than just a go-kart track in a parking lot (though to be fair, it is that too). You also have a mini golf course, a bungee jump (this is like a trampoline with bungees attached, not the kind where you jump off a bridge), a "fun slide", a game room and a "spider web" (where you try and maneuver through a maze, like on a Survivor challenge). Still pretty much in a parking lot, however.
Is it worth it? Eh, if you're looking for something different, sure. If you get lucky, you might even find some two-for-one coupons inside of the mall, generally around the area of Sea Life. That makes it even more worthwhile. And it does occupy a few minutes at a time - especially if you're playing mini golf.
But you're still in a parking lot.