I upgraded my 06 Prius to 205-60-15 BFGs on stock wheels. The tires weighed 5 lbs more per wheel, and I lost nearly 5 mpgs, but it was worth it for improved handling and wet traction. There are always compromises. I'm OK with the stock wheels on the CT. I only wish they weren't chrome. I'm not into bling chromes, and would prefer the stock alloys, or the dark gray available in Australia. I do like the wheels you are considering, just not as 19s.
A 19 will ride much worse, and probably lose a few MPGs, but it looks like you've already thought about that.
The stock wheels are a grey finish.If you have chrome then the dealer did that.
JMHO, I feel wheels above 17" are just for looks cause ride quality suffers big time with not much gain in performance , especially for this car.