You're not alone. I'm another prosumer who has been managing with his 2008 Mac Pro and is eager to buy one of these. I suspect my configuration will be in the $5k range but won't know until we see how they price configurations. Given the lifespan of Macs for me, I'm fine spending the money. I don't want an iMac, either. I've been on my 30" ACD for probably 10 years now. I'll replace it soon, but I don't need to buy a new monitor every time I buy a new computer, which is what the iMac forces you to do.
Btw, to your camera example, I also spent more on my camera than most sane people think makes sense. However, I have some priceless pictures from the camera that is directly related to its ability. Capturing just one of those pictures alone probably justified the cost difference in the camera to me. Computers are a bit harder to explain the value on, to be honest, but having capable equipment matters to me. Heck, I don't drive a Yugo, either.