There is no flat out benefit on working with Vectorworks on either a Mac or a PC specifically. As long as it has been properly configured, it will work identically on comparable hardware.
Mac and Windows machines are prone to different issues, I have equal calls and email issues from both camps pretty much, they just have different symptoms and solutions.
If you want a monitor as well, the current 5K iMac is an extremely good price since it includes such a high res display. The Mac Pros are excellent for working with Vectorworks, but unfortunately we do not yet support multiple graphics cards, so you are paying for more than VW can use.
Macs tend to have better resale value, but often have limited or no hardware upgrade options for anything other than hard drive and RAM. On the Windows side, resale is crap but it is easier to upgrade the graphics hardware later on if you go with a desktop configuration and that lets you extend the usable life of your machine significantly. So they both offer ways of either recouping or extending your money.
The ecosystems used to be significantly different, but many applications now work on both, or at least have equivalents. I use both constantly now and other than a few niche pieces of software (Screenflow on Mac) there isn't much I can do on one that cant be done on the other.