True, but realistically when purchasing any computer component, you can expect it to be outdated in a year. If you're a PC gamer, it's just something you get used to. For example, I'm selling my 6970 for about $150 less than what I paid for it last year to upgrade to the 4GB 7850. Depending on what I get for it (and what other cards of the same model have been selling for) I should be able to pay for the most, if not all of the 7850. I'll probably wait another year or two before I upgrade again. PC gaming is an exciting waste of money.
If you have to upgrade video cards every year, you either have unrealistic expectations or you are making unwise purchases.
6970 is still a great card for 1080p gaming. You have a 2gb, am I correct? the extra 2 gb of memory (on that 7850 you are eyeing) will make absolutely no difference at 1080p gaming, nor will it make a positive impact if you are doing eyefinity. 7850 is not really much of an upgrade at all for you.
In your case, I would definitely suggest waiting.
As far as any negatives on PC gaming, the money that you spend up front you make up on the back end with ridiculous steam and amazon sales. PC gaming isn't a waste of money at all for those that are really into it.