I'm just throwing out ideas here, not trying to sway one way or another:
I don't know what your dealers offer there, but a pretty good chunk can be taken off of MSRP on new Porsches (excluding special and GT cars). We've even custom ordered at 7% off. Having driven both extensively and been on and off track in both, and ridden with professional drivers in both at the PEC in Atlanta, the 718 is a technically superior and faster car.
I do also understand that the H6 without forced induction is the ideal Porsche. We've currently got a 981 Spyder, so I get the whole naturally aspirated thing. I just always felt my wife's 981 S felt held back or restrained.
I get that a good deal can be had on second hand; I'm just saying, there are some very good buys out there on new cars, at least in the southeast US. And I'm pretty sure the 718's come with more standard than the old base models, puts them pretty close to the used S as far as performance and equipment.
If you do decide pre-owned, in the states, the CPO warranty is basically optional... it is a flat fee to add it on or take it off, somewhere around $2k for the 981's. This may help with your negotiating if you decide Cayman.