Well there is the face lift and the fact that the Sport trim will be gone for 2018, so between those two that is enough to make a decision. I dont think it will be a guarantee either that you can get such a big discount from MSRP for the 2018's, atleast not initially.
Im not understanding this "depreciating risk" for the 2017 people are talking about. Any new car depreciates as soon as you buy it and face lift vs non face lift wont matter much down 5-10 years down the road selling it used. Unless you are the type who wants to sell the car very near term, only keeping it for a few years max, then 2017 vs 2018 would make a difference.