Based on experience I tend to be skeptical of anything a car dealer tells me. Dealer service departments always seem to be trying to upsell. I suspect the service writers are offered incentives for doing so, and it does not seem to be any different at the Porsche dealer.
That being said, can't say an alignment is a bad idea other than the potentially needless cost, but my reaction is that it's probably overkill unless you have reason to believe your car needs an alignment.
One other thing to point out. Given that you are buying Atturo tires, the cost ratio of the alignment to the tires is going to be unusually high (right now a set of four Atturo's from Simple Tire is only $531 delivered). Assuming you would be paying for an alignment to "protect" the tires from unusual wear, the worst case scenario is probably needing to replace a couple of tires if they are wearing incorrectly and you don't notice it. Given the very low cost of the Atturo tires, that would be far from a disaster. That's one of the reasons I'm willing to try the Atturos. If it turns out I don't like them (despite all the positive comments from forum members) it's not really a huge loss if I were to end up disposing of them.