BF4 ULTRA at 1080p will reach 2.1gb with 10% of supersampling, titanfall need 3.7gb for insane texture settings...as the games progress they constantly use better and better texture packs within the game itself with higher and higher resolutions and details in them, making them heavier thus requiring more VRAM to play the game at high settings...this is what makes new games and modded games looks better it is because they use better textures and this require more and more VRAM...but as i said it has nothing to do with processing power, for example running BF4 on low texture setting (NOT Anti-aliasing this is completely different, i'm talking texture resolution and texture filtering here) versus BF4 ultra texture settings the performance difference is only 1 or 2 FPS but the VRAM usage difference is major.
One good thing to note too is that the new consoles come's with an 8gb pool of DDR5 shared memory for the system and graphics ressources, so for example those consoles could use 4gb as standard RAM to store a game in use and use the other 4gb as VRAM for the GPU and display some very high quality textures, and you know what this is on awaiting to happen right on the next corner...you will quickly see new games with better and better textures hitting the market pretty fast in the upcoming months and years...
So if you ask me, yes defenetly a 4gb card is a good investment and is defenetly more future proof in the way that it will allow the user to display higher quality textures in his favorite games for a longer period of time...even at 1080p and even on a weaker card, as long as it can play games at 1080p with okay framerates it will be able to use high quality textures and high quality texture filtering (again not ANTI-ALIASING this is not the same, it kills GPU processing power...) i'm talking anistropic filtering, or texture filtering and texture quality here, don't get me wrong.