If you can get it cheap (ie: used) then go for it. It won't really affect the performance that significantly, but worth a try nevertheless.
If you can afford to buy a PC then that's great, but new hardware is expensive, and there's always better stuff around the corner.
What you need to be thinking is:
Am I happy with my current computer (Can I put up with it, does it do what I need)?
Would the performance increase justify the spend, e-waste and CO2 emissions of a new PC?
How good a PC can I afford now Vs. in 6 months/12 months?