I'm retired so I spend money only when necessary, but I just upgraded to v5. It took a few months, but I concluded that it was a necessity. In 1968 I was at GE programming an IBM 7090 in Fortran to design the antenna for the Pioneer spacecraft to Jupiter. The computer was the size of my current house and had a whopping 32 Kb of core memory. WOW! That was a really big machine back then - it would be another two years before HP would come out with the first 4 function calculator WITH A SQUARE ROOT FUNCTION!!! - for about $1000. What would that be in today's devalued dollar?
My current computer is a Dell XPS 8500 with 4 Gb of memory running Win 7 Pro. I designed stuff to go to Jupiter with a 32 Kb (and that was an octal, not hexidecimal) machine and could not imagine that my current computer could not handle a model station for my railroad. Hoping Rhino 5 and another 16 Gb of RAM will do the job.
One thing I noticed with the demo program is that v5 is a whole lot faster than v4. A join that would take 3 to 4 minutes in v4 is done in 4 - 5 seconds in v5. That alone makes it worth the upgrade...