I bought the 3,1 (after an opportunity to upgrade from a 2,1) for reasons of longevity. As a SysEng, and part time developer who dabbles in CAD in the off hours, my hardware demands are nowhere near 'pro' level. However spending 4k almost a decade ago on a reliable machine that I still use today to write this message on is quite a bargain. Especially compared to the near yearly upgrades or 'RMA situations' I have with the Dells/HPs that sit in the other rooms that run everything from NFS services, esxi, Mach3, and even games.
Given that a used 5,1 here still costs as much as the 6,1, I'm rather eagerly awaiting what the 7,1 will look like. If for whatever it costs, that investment will carry me for another decade, then it will be a sound financial decision for myself. Despite what a fair number of opinionated solipsists on here think in regards to semantics and usage cases.