Steering Wheel "Sluggish" and Not Returning to Center

My friend has a 06 Prius with about 85,000 miles.

Ever since he purchased the car (used) at about 67,000 miles, I've noticed that the steering wheel is slow to return to center and the steering lacks the "springy feel" of the low-mileage Priuses that I have driven. I noticed abnormal tire wear on the car so I suggested 4 new tires and an alignment-- which was done without any improvement. The front toe was set to 0, and the rear toe is minimal (0.05 and 0.1 on the LR and RR, respectively). However, I did not have a zero-point calibration performed at the time of the alignment.

There is no obvious damage or wear to the suspension, as far as I know. Recently though, the steering wheel has decided to clock itself to the right so I know it needs another alignment. It has only been 17k since the last one. Are there any parts that I should consider replacing before doing this alignment?

Thanks.

 

Pressures are set to 40F/38R. Lower pressures don't make much of a difference either.