In my humble opition, not much for most system configurations. The optimum hash table size for example doesn't change (much) as overall memory available increases. More memory is only useful in conjunction with more processor speed. It's also worth bearing in mind that certain operating systems can only utilize a certain amount of memory. Beyond that point it's pointless to have any more.
However, you have got a very fast processor there. If you had multiple processors each running with mulptiple hyper-threaded cores, and at overclocked speeds, then yes, buying more memory would at that point make a big difference.
The key point is that engines only really need a certain amount of memory. Once they have enough, more doesn't help that much.
How much better/faster will my computer play if I go from 8gb to 16gb or 32gb?
I have an fx-8350 processor, if that matters.
Thank you