So what specs would qualify as "blisteringly fast." Discounting the graphics card, you can't get the specs of a machine a whole lot higher than what you have now.
Oh, yes you can. You can buy enterprise-class processors and have assloads of cores. And my cores came from AMD, you could get cores from intel. Of course, you would have to spend vastly more money, which is why I didn't do that. I bought as much machine as I could get for just a few hundred bucks. The MB and case are refurbs, the video card is just a 750 Ti (Might upgrade pretty soon though, nvidia is getting ready to drop another budget board) and the processor is the middle-of-the-road version.
Yes, you can add more RAM but going beyond 16 GB is only going to be helpful for a small selection of tasks.
Mostly you could have a faster processor, in the real world even the new i5 is faster than this 8350. And of course, you could have vastly more GPU. Mine was just around a hundred, you can spend as much as I spent on my whole system on graphics. Or, as I considered briefly, you could have a couple of processors, each with more cores. But I decided that 8 was enough, even if I virtualize a couple of dual-core machines I still have enough left to get by and if I want to feed more VMs than that, I need to spend a lot more on storage.