I just went through this ordeal myself with much of the same thought process. Started with a local dealer in Columbus, OH. Their opening offer was insulting and I didn’t counter. Then started a discussion with a dealer in Dayton by telling them I was targeting 15% before incentives, for all of the reasons you mention (new model with more HP around the corner, etc.). That discussion stalled at 5% before incentives. Then found a dealer in Cleveland with 3 550s on the lot. Thought I was going to snag a $86K MSRP for around 7% but the car sold. Doubled back to the dealer in Dayton and found that that car sold, too. Started looking out of state and quickly realized that the time I was putting in to this was eating in to the $400/hr I charge as a lawyer. I finally ended up where I started with the original dealer in Columbus. I took delivery on 8/7/19 with no regrets. Close to 7% off before incentives. You’ll see my numbers posted on the recent deals.
I’ve seen several posts recommending holding out for 10-15% off before incentives. I’m skeptical of anyone who claims to have actually closed a deal on those terms. Perhaps I am just in a different market or lack negotiation skills. If there are still 2019s on the lot by the end of the year, I’m sure you can do better than I did.
I’m still facing the 2019 vs 2020 dilema with the Porsche 911. A local dealer offered a decent deal on a 991.2 spec’d to my liking. The 992 is a bigger evolution of the 911 than the engine upgrade in the 550, so I’m going to wait for the 992. I’ll drive the 550 in the meantime and hand it off to my girlfriend when I finally pull the trigger on the Porsche. Then all will be right in the universe.
As others have reminded me, if you delay a car purchase in the belief that the next model will be better, you might find yourself waiting a long time. At the end of the day, the M550 is a compromise vehicle. Its straight-line fast but will never handle like a true sports car. I’m not sure there is any measurable or meaningful difference between 460 and 520 hp in a sedan for daily driving. If you get a 2019 and end up with buyer’s remorse, slap a Dinan tune in it.