All non-gold versions of Blitz as well as Carnevil run on the same Seattle hardware. The graphics are the big issue here in terms of emulation as they are high-end 3dfx (something around the Banshee or Voodoo 4 era). Gold versions of Blitz and Showtime on NBC run on Vegas which is fairly similar. I believe Gauntlet Legends runs on hardware similar (or identical) to Vegas, but branded Atari.
If you want to play Blitz, it's far, far cheaper to find a deal on the actual arcade setup than to purchase enough PC hardware to emulate it. A Blitz 99 board working with HDD can be found for $70-100 in many cases. Of course, if you have other uses of that PC hardware, then it's certainly something to consider.
As far as RAM, the extra could be very usable as cache for the HDD/CD image. Be aware that Vista itself can eat up almost a gig if you leave the rather worthless eye candy on, and 32 bit Vista (and XP) can only effectively use 3GB in most single application scenarios due to the kernel/userspace split.