Not really. I can build a top end desktop PC in about 90 minutes and get it up and running in 1/2 a day. OS installation and configuration takes the most time. Once it's up and running it's pretty much maintenance free. I only use top end parts and in over a dozen builds (computers for friends & family) I've only had one defective motherboard at installation. I don't have to pay any money for a service contract (not that I've needed any, I can't remember and part failures in built systems). I've only done a little bit of pano work but my i7 build seems to handle stitching just fine. It's not clear in terms of how Adobe has optimized PS and whether the top end Mac Pro with 12 cores is needed.
I believe you, but at the same time you mention and I7. Building a Xeon computer with dual workstation graphic cards and PCIe SSD is not the same. Not all the component vendors carry them a so you need to add some extra minutes ordering
Back to the price issue:
People keep comparing build boxes with Xeon workstations. Normally is less expensive or competitive to buy from Hp, Dell or Apple that buying shipping and build the a Xeon workstation.
Also in the case of high end CAD you simply need supported configurations (you pay a lot for support, I am talking NX or Catia not autocad) .
Now if we are talking about a i7 box with a generic mother board and a GTX card …
Here is a compromised but comparison (they are an apple oriented site and did not mention about the performance difference of the ssds): http://appleinsider.com/articles/13/12/24/apples-new-mac-pro-a-better-value-than-the-sum-of-its-parts
And here other calculations, under the pressure of Slashdot : http://www.futurelooks.com/new-apple-mac-pro-can-build-better-cheaper-pc-diy-style/
Notice that this person does not use PCIe based flash but it's able to match the performance of the Mac by using RAID 0 (I am not sure about I/O per second).
I will not be surprised if buying Dell is better that buying the components too (or even better than the mac).
At today prices It makes no sense to build a workstation from components (for pricing, it could be that the person need something especific that Dell, HP and Apple do not provide) . Now, who needs a certificated hi performance workstation with Dual Cards?
I continue to believe, as you, that for most people an i7 and a high performance array and a pro monitor will do. Few people (audio pro, Red camera owners by example) actually buy PCIe cards (not talking about graphics).
Buying a good computer and changing more often is a better investment normally. You buy the old one to pay for the new and since your data is on the array switch time is not an issue. External arrays nowadays are faster than internal drives (and in the case of the old mac pro crazy faster than it) and have big capacity at low cost (use HD not SSDs).
So : It seems that the mac pro cost a lot of money but it's not that expensive, even more so if we factor the form factor (not because is great but because it's a custom tour of force)