Amen. One of our own, the late Uncle Frank, often observed "You can't buy game." Truth.The 24-70/f4 is probably worth as much now as it will ever be.
Instead, I suggest focusing on your ultimate lens choices based on NEED..... As indicated above, the difference in IQ between the f4 and f2.8 is small.....as is the DOF. But the size and weight are very different. I don't think I've ever used my f2.8 at f2.8! LOL! But I've left it in the bag due to weight.... Decide what you need - and don't chase what others think.