When you buy a system there is always some minimum costs besides CPU lets say its X.
Then there is CPU costs Y.
Price/perf of X+Y improves all the way to 230$ CPU:s on intel side, and I'm expecting that in this year the curve may move it all the way to 500-600$ CPU:s.
The 8 thread improved clock speed larger cache server CPU:s do have a nice performance multiple over the cheaper ones. But this year we may start to see 8 cores 16 threads around double that price or some what over double the CPU cost, but the system costs and performance difference would need closer analysis to determine if the optimum point of price/performance extends there also.

But for desktop users and some server users the normally used price/performance calculation isn't accurate description of situation. You really buy the improvement over old system.

(New performance-old performance)/(new system price)