It's close to two bills for the step up, is it worth it for the extra 2g of VRAM...

I asked myself the same question when I upgraded my monitor from 1080p HD resolution to 1440p WQHD. The GTX980 gave me a lot of FPS in HD and I just didnt want to give them up in WQHD. Because you can expect the 980Ti to get you roughly the same amount of FPS back that the higher resolution of 1440p would cost you.
 
If you are at HD resolution I'd save my money. Because upgrading now for a possible future investment in a better screen like 4k or whatever makes no sense, because by the time that happens the pascal chips hit the shelves with probably 8GB of HBM2 vram.
 
Also the only two games I've seen using more than 4GB in max settings are GTA5 and CoH2 (lol). In case of GTA5 it's probably because the engine does all this streaming of the environment and the game is a console port where programmers are used to use the 8GB of unified ram of the consoles as much as they want which leads to less efficient utilisation of the available vram. In case of CoH2 it's probably bad programming overall. And all this is in 1440p too which also adds to the vram usage.
 
So still I wouldn't bother with upgrading now unless I don't need the extra performance right now.