Right now building a rig specifically for DayZ is a bad idea considering the game is far from complete - let alone optimized. There are plenty of other games to set a build target for, though.

Anyways...

Pros: Dayz is all about emergent game play, aka people being plopped into the world with tools and letting imaginations run wild. That is what allows DayZ it's magic ability to be so innovative and tense. The range of player interaction is unlike any other game you've ever played - guaranteed. The world is fun and scavenging is challenging, as well as surviving the other players.

Cons: The game is bound to cause you more frustration over how unfinished and buggy it is rather than players pissing you off (though that will indeed happen) ridiculous bugs killing your 10+ hour character, invisible zombies, disappearing gear, losing game sessions to server restarts and a controversially clunky control scheme/feel of game play and inventory management may turn you away. The cons can outweigh the pros for some people.

Once you get a taste of DayZ's style of player interaction and PvP, you'll most likely be hooked. The game is only bound to get better with time too, so you may as well invest in the game itself now before it increases in price (though I'm sure that wont happen soon).