This program is all about the speed of a single processor core. Everything else comes second, from a performance standpoint.
The reason many find somewhat older PC's running it better is because the program isn't terribly demanding of a video card, but is extremely demanding of a processor core (only 1 core, to boot).
midrange dual, tri, and quad core processors from within the past couple years tend to have great multitasking ability but each individual core is usually 3.4GHz or less (mainstream i-series, phenoms, etc.). Go back a couple more years and you find processors with fast single cores often well above 3.4GHz (athlon 64's, whatever intel was selling during that time period [lol], etc.)
Happened to me. I replaced my AMD 4000+ with a quad core phenom (and a whole new PC around it, too) and my universe sandbox performance took a big dive. Waiting impatiently on the upcoming multicore processing patch. =D