Mine is fine with the 17" wheels no wander at all and does handle quite well for a non-sporty hatchback, although they are noisier than the 15". I believe the steering has a different ratio with the 17" wheels, which may be something to do with it.
The U.S. Prius V (five) has 17" wheels with 215/45 tires. It has a faster steering ratio which is almost a full turn less from lock to lock. It also has a more powerful brushless steering motor, some different suspension components, and slightly different alignment specs. That could be why I have never had any of the issues described in this thread. I drove almost 600 miles today in gusty winds and rain, car was very stable and a pleasure to drive. Now if I could just get all the rattles fixed.