Fwiw, the thread is about the sales of the new Z4
models, not leases.
Regardless, lease programs don't change the fact that the new Z4 and the Boxster are much closer in MSRP than was once the case. Last time I looked, it seemed they were less than $2k apart on the low end, and within $3k-$4k on the high end.
When you're talking about high $40's to mid and upper $50's for what many see as a weekend toy, I can assure you that the price difference is of no consequence.
There's also the issue I mentioned re quality and reliability. As hard as it may be to believe, BMW seems to consistently rate average or slightly lower than average in every poll I recall seeing in the last 2-3 years while Porsche seems to consistently rank fairly high. That makes it even easier for some to accept the cost of the car to be a few thousand more.
But it sounds like you only want to talk about price, when my comments more than anything had to do with who has the best "sports" car. I'm happy with my Z4 too (the outgoing M variant), but I'm not going to sit here and say the idea of owning a Porsche isn't an interesting thought. As I said, and which applies to me too, Porsche just has a much better reputation at building sportscars.
There's room for both, and each will find customers. But they will be customers with different means and different needs and wants.