"More is better" as the current pitch line of a certain US cellular carrier says. For computers the "more" benefits are obvious for things like disk space, memory, CPU cores and network bandwidth. The same holds true in the virtual world: virtual PCs like to have more as well.
As a point of interest I recently conducted a very informal speed test between two identical virtual machines. My only (big) variable? RAM. One machine had twice as much RAM as the other. My goal was to see how much the extra RAM would benefit me during set up of a new virtual machine (even if that machine were destined to be allocated less RAM once it was up and going). Temporarily adding RAM should translate to a shorter set up time but would it be enough of a difference to bother with?...
