Heckler & Koch Pistols, HK Handguns, H&K Gmbh, then IMO its a no brainier, get the new one. The new one will come with a full lifetime warranty from H&K. Hell you'll spend $200 in ammo in just a few months if you are going to use it like your post implies.
Lifespan means different things to different folks. One example, is in the last few years Todd Green has run several H&K's to 50,000+ rounds with very limited maintenance. I'd be thrilled with 50,000 rounds of ammo, because even at $10/box 9mm, that would be $10,000 in ammo, and if you are shooting 40, or 45, a lot more.. At that point the $1000 pistol is cheap by comparison.