Something always bottlenecks something else. That's just the nature of PC.
Your 750Ti most likely will perform much better with, say an i7 6700K, but by how much? I'd guess about 15-20% better.
How much this correlates to actual gaming performance? Say you had about 60FPS on medium with your i3, my guess the i7 would gives about 70-75FPS better while still on medium.
So in this sense, it all down to this: if you are being comfortable enough to what you're at right now, why even bother?
Besides, rule of thumb on PC world; a better GPU would have more profound impact on graphical department long before CPU would.
tl;dr: it won't.