It might be worth it if youre looking to play with the absolute most eye candy you can get on the newest and most demanding games. Ive got a pretty heavily overclocked GTX670 FTW and while its a great card, I have to turn a couple settings down a notch on Crysis 3 and cant run Tomb Raider with TressFX without occasional dips down into the low 30's and even high 20's. Turning TressFX off though fixes this though and Im back up in the 50-70 fps range. Hitman Absolution slowed a little too on my rig. And Metro of course, while playable at max settings, is in the upper 30's most of the time.
Now while this is definitely 1st world problems and Im still getting great frame rates and its only these 3 games that Ive not been able to peg everything out at max, Id like a little more horsepower.
For 1920x1200 something like a GTX780 would not be overkill IMO. Nor would a R9 290x. Either one would be a very nice upgrade.
Now if youre not interested in getting the most eye candy possible from the most demanding games and dont mind turning a setting or two down in a very small handful of games, then your GTX670 is still a perfectly capable card and youd be better off in saving your case. Most people dont want to drop $400-550 just to increase performance on the top 1% of games. I do on the other hand and just need the spare $400-550 to do so. Its gonna happen one day. Got a power supply and CPU upgrade to do first.