I have an early '08 (8 core, 16 GB of RAM) and it is still faster than most desktops being sold today. The boot drive went bad so I bought an SSD, but haven't stuck it in. I run three displays off it - a 30" and two 24". I code, so this works fine for me.
I need the RAM less than I need the CPUs - I run multiple VMs to work in. OSX as the host, Linux and different versions of Windows depending on the project.
For what they are, MacPros are fairly competitive in price - try pricing a Wintel machine with 4 to 12 cores with up to 64 GB of RAM capacity and 5 drive bays, and able to drive 6 displays. Finally, find one that will run OSX.
House payments? Two. And I will earn it back in less than a month. Plus it is tax deductible.