Luigi's Flying Tires is not the old flying saucer ride, and was built to accomodate more than one passenger, as well as adding bars for safer loading and unloading. It allows parents to ride with small children who couldn't have experienced the flying saucers. I think its a good attraction for Carsland, to make sure that there are rides that little kids can go on and which aren't too fast. Little kids will love this ride as much as Dumbo.
I think teens and adults will like this ride as well as it is hands-on like Autopia, and it will interest guests who want to ride it again to perfect their tire riding ability. For the guests who want to sit back and let the computer do the driving, like in RSS, then this ride might seem like too much work.
That being said, there is a plan B, if the tires just prove to be too unpopular by having too long lines, as there is plenty of space behind this attraction to improve the ride by making major changes to it. I don't see this happening for a while as everybody will want to experience it at least once.