SLK holds no appeal for me at any price range. The Z4 on the other hand, really sucked me in. The trick, IMHO, is to custom order the car optioned like you want and get a good deal. My S30i with M/Ivory, heated seats, and iPod/USB came in around $51K after haggling, and that is reasonable. As equipped, it captures the core traits of the car, and the ivory/athracite interior looks like a million bucks.
It is interesting that the same basic car runs the range from about $47K all the way into the $75K range, and can take on the role of a basic roadster all the way up to a cushy optioned luxo barge. Lots of choices for a range of buyers. Knowing how efficient BMW is at dealing with production variations, I figure they must have that range to maximize potential of the vehicle. I might think the car makes the most sense with M package around the low $50K range, but why not let a customer come along and pour money into the options sheet and buy that $75K model if they want? In the end, it's just more profits for BMW. They wouldn't offer it if there weren't at least a few buyers lined up to drop that much $$.